The Monokaki Family gathered in the room in the underground maze, all staring in shock at the body of Ryouichirou with a stake stuck through his chest. As soon as we'd found his body, we left the basement and went to call everyone in the mansion. When we explained that Ryouichirou had been killed and everything that had happened to us leading up to our finding his body, they all looked shocked. The door to the archive had been kept open by the doorstop, just like it had been yesterday, so just like yesterday, we passed through and descended through the trap door to the basement, where we led everyone to the room.
The area around the body was filled with a thick scent of sweet olive. It seemed like a large amount of perfume had been sprayed.
Next to Ryouichirou's body was a another opaque black glass die, exactly like the ones left at the previous crime scenes. I approached the body and picked it up. Then I confirmed that the stake had pierced Ryouichirou's heart. There appeared to be an LED light in the base of the stake, which was currently lit up green.
“Hmm, this is...” Camembert approached the body and looked at the stake stuck in its chest. “No matter how you look at it, this stake is the murder weapon. The murderer used it like a knife and stabbed Ryouichirou in the heart.”
“No,” said Mei. “I think they used the air rifle.”
“Air rifle?”
“Yes, the one kept in the storeroom.”
“Oh, we did have one of those, didn't we?”
Camembert looked convinced, but I was completely lost. Mitsumura didn't look any better. Seeing us like that, Mei explained to us.
There was an air rifle stored in the mansion's storeroom, and that gun fired bullets shaped like stakes. Mei said that she, Yozuki, and Teika had seen the gun in the storeroom last night, and told us in detail what had happened.
After hearing her story, Mitsumura nodded in understanding. Then she asked “Can you show me around the storeroom?”
Mei nodded and started walking towards the entrance of the underground maze. We both followed behind.
It seemed impossible to get to the northern section, where the storeroom was, without passing through the mansion's living room. So we did and walked down the hallway beyond until we arrived in front of a certain room. It had an automatic door, and when Mei pressed the button next to it, it slid open. It was a long room, 40 meters deep with a wire mesh ceiling, and a two meter tall automatic door was installed on the northern wall at the back of the room.
“That must be the storeroom over there.”
Mitsumura said that as she approached the door to the storeroom and reached for the button next to it. For some reason, Mei appeared to panic and tried to stop her. But Mitsumura didn't notice and pressed the button with her index finger. And as soon as she did...
An ear-splitting siren rang out.
Mitsumura quickly covered her ears with her hands. We followed suit, panicking. But the thunderous roar of the siren pierced right through our hands, tormenting our eardrums with a roar so loud we feared it would knock us unconscious.
Mei managed to hit the button again, and the sound finally stopped as the door closed. The sudden silence left me with ringing ears that were almost as bad.
“What was that?” Mitsumura asked.
“It was the alarm,” Mei replied, pointing with her index finger. “There's a huge siren next to the mansion, remember? That sound was that siren going off.”
Come to think of it, outside the mansion – or rather, outside the shell containing the mansion – there was a siren on top of a ten foot pole.
Mei nodded at us and continued.
“There's a security system installed in this storeroom that activates from midnight to 8:00 A.M. every day. And that security system is linked to the siren outside the mansion. If the door to the storeroom is opened during that time, the siren will ring until the door is closed. And as you just heard, it is very loud. I've heard the siren a few times in the past, and you can easily hear it from anywhere in the mansion, or even in the whole of Yatsuwako Village. The siren's volume is 170 decibels, about the same as a space shuttle launching.”
That was too loud. Mitsumura frowned and said “I wish you'd told me that earlier,” clutching her sore ears. Then she looked at her watch.
“It's 7:50 now. The security system should be deactivated in ten minutes.”
“Well, I vote we wait,” I said. I didn't want to deal with listening to that noise the whole time the door was open. “By the way, is there any way to turn off the security system?”
“There isn't,” Mei said, which was about what I expected.
So we waited in front of the storeroom for ten minutes. Then, when the clock struck eight, we opened the automatic door and stepped inside.
Sure enough, the air rifle was inside the storeroom.
“There it is,” said Mei.
“That's the same place it was yesterday,” said Yozuki.
“But,” said Teika, “the seal on the muzzle's been removed.”
From what I'd heard earlier, the muzzle had been sealed with paper before dinner last night. But there was nothing there now. The culprit must have torn it off.
And there was one more change. Last night, that air rifle had been connected to the wall of the storeroom by a chain, but now, that chain had been cut in two by something like a pair of wire cutters. Mitsumura picked up the two halves of the chain, fit their ends together like puzzle pieces, and announced her findings.
“The surfaces of the cuts match. So then, does that mean the culprit cut the chain and took the gun, then used it to shoot Ryouichirou before returning it to the storeroom?” Mitsumura turned to Mei. “By the way, are there any other guns like this one?”
“No, there aren't. This gun is custom made; there is only one like it in the entire world,” Mei replied. “Apparently, it's an extremely complicated weapon created by a Swiss manufacturer, impossible to replicate.”
“I see. So, where are the bullets?”
“Over here.”
Mei opened one of the wooden boxes. Indeed, inside were about ten stakes. So, those were the bullets for the air rifle.
“Hmm...” Mitsumura scrutinized the bullets, then raised a nitpick. “There isn't any way we can rule out the possibility that the bullet was stabbed directly into the body like a knife, is there?”
The tips of the stake-bullets did look very sharp, so they could have been used like a blade.
“But you see,” Mei said, shaking her head, “there's no way that bullet could have been stabbed in by hand. That's because the LED lights on the base of the bullets only light up after they've been fired from the air rifle.”
Come to think of it, there was a green light on the base of the stake lodged in Ryouichirou's body. The system probably worked by sending a signal from the gun at the moment the trigger was pulled, which turned the light on when it was received. In other words, determining whether or not the bullet had been fired from the gun was possible just by checking the light.
“But,” Mitsumura insisted, “It's possible the bullet was fired at some other time, retrieved, and then plunged into Ryouichirou's chest, isn't it?”
Mei once again shook her head and denied it.
“No, that isn't possible, either. When the bullet hits an object, a three centimeter long barb shaped like a cross shoots out from the tip. Which means, if you shoot a person with the gun, the barb gets caught in them and it can't be removed, and conversely, if you were to try to stab someone with a bullet that had its barb extended, it would get in the way and you wouldn't be able to. And if the barb is broken, the light on the bullet will go out, so that method can't be used, either.”
So, once the bullet was fired, it couldn't be stabbed like a knife afterwards.
Hearing Mei explain it so clearly, Mitsumura looked at her suspiciously. “You certainly know a lot,” Mitsumura joked. Mei shrugged and said “I just read the manual,” then showed us a booklet from the storeroom. I'd thought she was joking, but apparently we were also allowed to check out the enclosed instruction book.
“Hmm, I see,” Mitsumura said as she flipped through the manual, then picked up one of the bullets in the box. “May I try it out?”
She picked up the air rifle and left the storeroom with it still in hand. She marched straight to the door. Everyone hurriedly ran after her, but Yozuki suddenly stopped, tilting her head to the side.
“What's the matter?” I asked.
“Is it just me,” Yozuki said with a puzzled look on her face, “or is the seal on that door broken?”
“That door?”
I looked where Yozuki was pointing and saw a huge metal door on the east wall of the room. It had a pair of elevator doors that opened to both sides, with each door being 15 meters tall and 7.5 meters wide, for a total of 15 meters there, too. The two doors definitely bore the remnants of a seal made from talismans. But the talismans had all been torn. Someone had opened the door. But what did that mean?
Yozuki spoke with pride.
“You see, that door was sealed before yesterday.”
“The door was sealed?”
When I looked at her suspiciously, Yozuki got even smugger.
“Yes, it was sealed. Behind the door was sealed... a monster.”
“That is... a major development.”
“There's also a rumor that if you open it, you'll die.”
Was this girl okay?
“She's telling the truth.”
Mei explained the situation to Mitsumura and I. It seemed everyone else already knew.
After hearing to her story, Mitsumura looked interested.
“So, someone opened that door. And thinking about it logically, it must have been the culprit.”
She was right, that door was supposed to have a curse that killed you if you opened it. Nobody who wasn't planning something bad would even think to open it.
We approached the door, with Mitsumura leading the pack. When Mitsumura drew close, her eyebrows raised.
“The glass case over the button has been broken.”
She was right, the button next to the door had a glass case over it, but there were traces that it had been shattered by a hammer or something similar. It must have been broken to press the button.
“That case was definitely intact yesterday evening,” said Yozuki.
So, the case was broken after yesterday evening. The person who'd broken it and opened the door was likely the culprit behind all the murders that had taken place over the past few days. The question was why they'd opened it.
We looked at each other and decided to open the door. Even though it was a door that would curse you to death if it was opened.
Mitsumura pushed the button on behalf of the group. After a few seconds' lag, the metal doors slid to the side, revealing what lay within.
We all held our breaths.
We were inside a huge, concrete cube of a room, each side measuring 15 meters. However, there was nothing in the room: not even a floor. Where the floor should have been, there was a huge, square, 15 x 15 meter hole.
We were suddenly confronted with a huge hole. Everybody gasped when they saw it.
On the edge of the hole was a set of stairs leading underground. They were simple metal shapes, like the emergency stairs on the side of a building. Mitsumura turned on her smartphone's flashlight and led us down the stairs. At the bottom of the stairs was a vast underground space.
It was another limestone cavern, but this one was incomparable to the one containing Yatsuwako Village. The ceiling was easily a hundred meters high, and we couldn't even tell how vast it was – we'd reached the bottom of the stairs and were standing by one of the cavern walls, but we couldn't even see where the far wall was. This was the true underground empire. I couldn't believe such an enormous cavern could exist in the natural world.
There were lights on the ceiling of the cave, and as we descended, they switched on automatically. And within that underground cavern stood a single rectangular structure. Specifically, a rectangular hut with a door and a window, about the size of a one-room apartment. I approached the building and tried to open the door, but it wouldn't budge. The door opened into the room, but something was blocking it from the inside.
“It's stuck,” I said.
“Hmm, I wonder what it is.”
Yozuki didn't sound at all worried and ran around to the window on the east wall of the building, which was fixed and couldn't be opened. What she saw there rooted her to the ground.
“Kasumi, look...”
Yozuki pointed into the window and asked me that. The air was suddenly very ominous. I approached the window and looked through. And like Yozuki, I immediately froze in shock. Inside the building, in a room about ten tatami mats in size, lay the dead body of Kyoujirou Monokaki, a knife lodged in his chest.
The day before yesterday, when Ryouichirou had tried to hit him with a stun gun, Kyoujirou had run away and been missing ever since. So the culprit had found him, killed him, and brought him to this room.
“Why are...?”
But there was something even more interesting about the room than the dead body.
Colorful wooden boxes painted in bright colors. Tons of them had been placed in the room. They came in a variety of different sizes, and each was painted a single solid color: red, blue, green, or yellow. It was those wooden boxes that were blocking the inward-opening door, keeping it from being opened.
“This is...” I groaned.
It was a bizarre locked room. We decided to call it the Locked Room of Four Color Boxes.
When we broke the window and entered the room, we confirmed that Kyoujirou was, in fact, dead. The room was filled with the painted wooden boxes to the point where there were almost no gaps, so the only way to move was to walk over the boxes themselves, but there was a large, box-free gap in the southeast corner of the room. Kyoujirou's body was lying there.
“These wooden boxes,” Mitsumura began, looking around at our group. “Does anyone recognize them? For example, were they kept anywhere in the mansion?”
The members of the Monokaki Family all turned to each other, then Mei spoke on their behalf.
“No, we've never seen them before.”
“I see. So, what that means...” Mitsumura put her hand on her chin. “Is that these wooden boxes were here from the beginning. The culprit knew in advance that these boxes and the room where they'd commit the crime were here in this underground cavern. That's why they broke the seal of the off-limits room, so that they could use these wooden boxes to create this locked room.”
That was certainly how things looked.
“But Mitsumura,” Teika asked. “How could the culprit have known that?”
“Yes, that's another mystery...”
With that, Mitsumura began looking around the scene, and her eyes fell on the northeast corner of the room. That area was naturally full of wooden boxes, but on top of the box there was a black glass die. Mitsumura stepped over the boxes and came back holding the cube. It was a cube with sides of about 3 cm each, but this one was a bit different. The cube had been cracked, and some of the glass was missing. And as a result, we could see for the first time that the cube was hollow. In other words, it wasn't a cube, but a box, and inside was...
“There's something in there,” said Mitsumura as she peered into the box through the glass. Then she took out her Swiss Army knife, thrust the blade into the crack, and levered it open.
She shook the box, and something fell out of the widened crack. It was a small, folded piece of paper, and when Mitsumura unfolded it, her eyes shot open.
“Well, that's one mystery solved,” she said, showing everyone the piece of paper she'd unfolded. It was about the size of a memo pad, and the following was printed on it:
Locked Room Draft No. 8 (By one of the Eight Locked Room Masters of the Showa Era: Kunihiko Hitsujiya)
The victim's body is discovered in a room. The room is filled with a large number of wooden boxes painted in bright colors, preventing the inward-opening door from being opened or closed.
We all stared at the paper as though we were afraid it would vanish. The locked room described on that paper bore a close resemblance to the scene of the Locked Room of Four Color Boxes right before our eyes. And the Eight Locked Room Masters of the Showa Era? As in, the eight legendary mystery novelists who'd been brutally murdered in this village long ago and were now enshrined as the composite deity Yatsuwako Myojin?
The paper with that text written on it was contained in a glass cube that had been found at the scene. That wasn't the first cube like that we'd found. Five had been found so far – no, seven, if you included the ones we'd found in Saboten Iyokawa's room.
In other words, when you paired the one found here in the Locked Room of Four Color Boxes, it was eight.
Without any conscious effort, the same thought passed through all of our mind.
“I'll go get the others.”
I said that and immediately left the building containing the Locked Room of Four Color Boxes. Since no one else had wanted them, I'd been left in charge of the black cubes. I hurried back to the room in the mansion where I was staying to get them, then returned to the others, completely out of breath. Everyone was waiting outside the Locked Room of Four Color Boxes, right next to the window we'd broken to get in, so I lined up the black cubes on the cave floor. I added the one we'd picked up at the scene of Ryouichirou's murder, and then there were seven.
“Good job,” Mitsumura congratulated me, then said “Well, let's get to work” and pulled out a fist-sized rock she'd picked up from somewhere in the cavern.
After she smashed the seven cubes, seven pieces of paper came out, as we'd expected.
Locked Room Draft No. 1 (By one of the Eight Locked Room Masters of the Showa Era: Akira Nezumiyama)
The victim's body is discovered in a room. The door has no thumb turn, and a key is required to lock the door even from the inside. The key is found next to the body, and a huge “Y” is drawn in water on the floor of the room.
Locked Room Draft No. 2 (By one of the Eight Locked Room Masters of the Showa Era: Inori Ushizaki)
The victim's body is discovered in a Japanese room. The victim's head has been severed at the neck by a blade, producing a violent spray of blood. The blood sprayed upon the sliding doors has dried, preventing the doors from being opened or closed.
Locked Room Draft No. 3 (By one of the Eight Locked Room Masters of the Showa Era: Umeka Torahara)
The victim's body is discovered inside a room. The keyhole is blocked, and a glass jar has been placed over the lock on the inside of the door. There is a secret passage beneath the room, but it is lined with spiderwebs, making it impossible for anyone to pass through.
Locked Room Draft No. 4 (By one of the Eight Locked Room Masters of the Showa Era: Eisuke Uno)
The victim suddenly catches flame in full view of the public. This qualifies as a locked room, as nobody approached the victim at any point prior to the flame's ignition.
Locked Room Draft No. 5 (By one of the Eight Locked Room Masters of the Showa Era: Ouki Tatsuda)
The victim's body is discovered in a massive indoor maze. Inside the maze, several guards sitting on metal chairs are posted, but the culprit is able to make their way through the maze without being seen by any of them.
Locked Room Draft No. 6 (By one of the Eight Locked Room Masters of the Showa Era: Kairi Mito)
The victim is found hanged in a storehouse. Both of the victim's legs were cut off at the thighs, then reattached with duct tape.
Locked Room Draft No. 7 (By one of the Eight Locked Room Masters of the Showa Era: Kyoko Umayado)
The victim's body is discovered inside a room. Their throat has been slit, and there is a large pool of blood next to the body. Wooden boards have been nailed over the door, making it impossible to enter or exit.
Mei spoke breathlessly. “This means the culprit is committing the crimes using tricks devised by the Eight Locked Room Masters of the Showa Era?”
Though we were already familiar with their fates, we felt a new chill of fear. The Eight Locked Room Masters had gone on a trip to the inn of this village to write a novel together. Each of them was to prepare one locked room trick. However, they were brutally murdered, right there at the inn, and afterwards, the eight tricks were all stolen by someone.
And somehow, those eight tricks had found themselves in the hands of the culprit of this case, and they were using them to kill, and kill, and kill... It was as though they were possessed by the ghosts of those dead writers – the Eight Locked Room Masters of the Showa Era.
“But one a' these drafts is a bit weird,” said Teika with a tilt of her head. “Look, at Draft No. 5.”
Indeed, looking over it, that draft was strange. From the description of “a massive maze”, it was clearly supposed to correspond to the scene where Ryouichirou's body was found, but there was a major problem with that. That was, of course, that there weren't any guards sitting on metal chairs in that maze.
I tried to remember how the archive had been that morning. The entrance to the underground maze where Ryouichirou's body was found was in the floor of the archive, and the door to the archive had been left open by a door stopper. That meant that anyone could enter or leave the archive, and by extension the maze, whenever they wanted. It was the furthest thing from a locked room imaginable.
“But,” Yozuki interjected, “there could be something we've all overlooked, so wouldn't it be better to check later?”
By Yozuki's standards, that was pretty reasonable. So I gave a reluctant nod, then looked back into the room through the broken window, facing the problem before us now. It was a strange room, its door blocked by colorful wooden boxes. Gazing into the crime scene, I mumbled something to myself.
“Why did Zerohiko Monokaki build a place like this beneath his mansion?”
The man who'd built this mansion was Mei's grandfather, Zerohiko Monokaki. Since that was the case, it was safe to assume that Zerohiko had also built this room, which was the scene of the Locked Room of Four Color Boxes. In other words, Zerohiko Monokaki had somehow gotten his hands on the locked room drafts left behind by the Eight Locked Room Masters of the Showa Era, and prepared the scene of one of them, Locked Room Draft No. 8, that is, this room here in the underground space, in real life. He'd built a hut in a limestone cavern and prepared colored wooden boxes to fill it. But what was his purpose for doing so?
“That much is obvious,” Mitsumura said in answer to my question. “The reason he'd go to the trouble of building such a room beneath his mansion... It's obviously to commit a locked room murder.”
He built this room for the sole purpose of killing someone in it? We were all shocked by Mitsumura's argument. But when we thought about it... We'd concluded that the Locked Room of Human Combustion where the young villager Murawaka had been burned to death was committed using a Gungnir, a machine invented by Zerohiko Monokaki. Naturally, a machine like that wasn't easy to obtain, but for its inventor, the fantastically wealthy Zerohiko Monokaki, it would be a different story. Zerohiko would have been able to prepare a Gungnir to recreate the Locked Room of Human Combustion – that is, Locked Room Draft No. 4. Or, rather, he was the only one who could prepare it. If that was the case, the theory that Zerohiko was planning to commit murder using the tricks created by the Eight Locked Room Masters of the Showa Era didn't seem so far-fetched. And although the plan had been temporarily thwarted following the death of the mastermind, Zerohiko, what if the culprit had managed to obtain his notes, containing the eight drafts of the locked rooms and the details of the plan – a notebook or something like that which also contained information about the plan for this Locked Room of Four Color Boxes?
It wasn't an impossible story. If that notebook had been left behind, it must have been somewhere in the mansion. It was entirely possible that the culprit coincidentally stumbled on it and took the plan for themself.
When I said all that, Mei put her hand on her chin and said “I agree, it is possible.” She looked gravely serious.
“Zerohiko Monokaki was planning a locked room murder – and the intended victims may well have been us of the Monokaki Family. It's entirely possible. Because Zerohiko Monokaki was a man whose mind was consumed by locked rooms.”
“Consumed by locked rooms?”
“Exactly as I said,” Mei replied. “Zerohiko Monokaki read too many locked room mysteries. Most of his brain was filled with nothing but locked rooms. Zerohiko's mind was taken over by the concept of 'locked rooms' – or perhaps by the God of Locked Rooms itself.”
“How many stories have been written in human history featuring locked room tricks? No one can say for certain. Hundreds of thousands? Millions? It's such a large number that nobody can grasp its totality.”
After suddenly beginning like that, Mei raised her index finger and said “However.”
“There is an urban legend that tells of a library. Somewhere on Earth, there is a phantom library containing every locked room mystery ever written. It's called the Locked Room Library – not to be confused with the famous locked room agent, the Living Locked Room Library. Some stories place the Locked Room Library in London, others in Buenos Aires, still others in Canberra. Nobody knows for sure where it is, and whether it even exists is unclear. But if you believe Zerohiko Monokaki, he once visited the Locked Room Library. When he was in his fifties, he spent ten years reading every locked room mystery in the world.”
“He read every locked room mystery ever written?”
I couldn't help but find that story a bit suspect. The idea that the Locked Room Library existed at all was dubious enough, and reading the hundreds of thousands, possibly millions of locked room mysteries in existence didn't seem possible for a single person, even if he did take ten years.
“It is possible,” Mei said without lowering her finger. “Because Zerohiko Monokaki had mastered the skill of the 100 Readings.”
“100 Readings?”
“It's a super-speed reading technique that allows the user to finish any novel in 100 seconds,” Mei explained. “In that case, simple math would show that he could read 36 novels in an hour. Zerohiko used that skill to read every single book contained in the Locked Room Library, twenty hours a day, 365 days a year, without taking a single break.”
“Well, that's just what he told us,” Mei added. If all that was true, Zerohiko had read 2,628,000 locked room mysteries in ten years. That did sound like enough to have read every locked room mystery in the world. Not that the story had become any easier to believe.
“Well, regardless of whether or not the story is true,” Mei said with a shrug, “It is true that when Zerohiko returned from his trip to the Locked Room Library, his personality had changed completely. Before, he was a normal person, excepting his excessive pride, but when he returned, he lost interest in everything except for locked rooms. He no longer cared for money or status, and he didn't value anything but the fame that came with creating a great locked room.”
We all held our breath in silence. Was it really possible that a man's personality could change that much just from reading too many locked room mysteries? Teika finally interjected “I suppose it's possible, in theory.”
“A person's personality is pretty dependent on their memory. If the people around ya lie and cheat ya too many times, you'll become more suspicious, and if ya grow up surrounded by love and charity, you'll become a good person. Ya could say that when a person thinks, they're reading through a database of memories and runnin' a program on the OS called yer brain cells. Naturally, the result of the output depends on the contents of the memory. So if there was a person who'd read 2,628,000 locked room mysteries, who'd painted over all their old memories with locked rooms...”
“It would birth a person who could only think of locked rooms?”
It sounded like some sort of sick joke. But... Zerohiko Monokaki once wrote a novel called Murder by the Spear of God, featuring the infamous machine Gungnir. That book had been an alibi novel. That meant he had once had a certain amount of tolerance. Tolerance for mysteries other than locked rooms. Had he lost that tolerance after having his mind corrupted by the locked room?
“At any rate, when Zerohiko returned from the Locked Room Library, his brain had been completely consumed by locked rooms,” Mei reiterated. “One day, he suddenly announced that we were all moving to Yatsuwako Village. We all found that a surprise. We wondered why Zerohiko would do something like that. But thinking about it now, it must have been to prepare his own murder plan.”
Mei gave a firm nod. Thinking back, Yozuki had told me that Zerohiko had been paying all the villagers' living expenses to keep the village from being abandoned. In light of what we knew now, that must have been to preserve the existence of Yatsuwako Village, where his murders would take place...
Wait, no. That didn't make sense. It didn't explain why Zerohiko was so obsessed with Yatsuwako Village. It was true that the superstitious populace made the village the ideal place to create a closed circle using the “curse” of the spontaneous human combustion trick. But it seemed strange he would have moved to the village just for that reason. Was there some other reason he had to use this village as the scene of his murder drama?
And there was one other strange thing: Zerohiko's death. Zerohiko had ended his own life by shooting himself with a gun. It was strange he would have done that before committing the series of killings in Yatsuwako Village he had planned. Zerohiko had committed suicide in front of his entire family, so there was no way he'd actually been murdered, but if that was the case, why had he had to die? That question refused to leave my brain.
When I looked over to Mitsumura, I saw her resting her hand on her chin, looking to be deep in thought. I had a feeling she was thinking the same thing as me.
The next thing we all did was investigate the Locked Room of Four Color Boxes. We considered the possibility that the culprit was hiding inside one of the boxes.
All of the boxes had thin lids, so we split up and removed them all, but nobody was hiding inside any of them. But they did contain something else: water and round stones the size of softballs. However, even though there were twenty-six wooden boxes in the room and all of them were full of water, only eight of them contained the stones.
We all found that puzzling.
Maybe the culprit had run a hose all the way down to this underground cave and filled the boxes with water. Or maybe the water had been in the boxes since before this underground area was sealed.
But neither of those explained why they'd been filled with water, or what the stones meant.
After we finished investigating the Locked Room of Four Color Boxes, we decided to properly explore the rest of the underground limestone cavern. The cavern was shaped in a rough square, about 100 meters high, 5 km long, and 5 km wide. Of course, that was an extremely rough estimate based on how long it took us to walk from one end to the other. The cave had a circumference of 20 km, and we split into two groups and walked around the perimeter each way. The space was completely enclosed; neither group came across a single side path. However, at the point where the two groups met up, that is, the exact opposite side of the cave from our starting point, there was a huge square iron door, about 80 meters to a side, in the rock wall. I'd never seen such a big door in my life.
“It's like something out of the Arabian Nights,” said Yozuki. “Open sesame!” The door ignored her.
Of course, the actual way to open the door was the button installed next to it. Another automatic door. The door had a circular sub-door like a manhole cover at about waist height, but when I checked, I found that it was locked and didn't open.
But the main door might have. So Mitsumura hit the button, and after a few seconds, the huge iron door slowly started sliding outwards.
The dazzling light that came shooting out made us all cover our eyes.
It wasn't artificial light. It was a heavenly glow none of us had seen in days. That... couldn't be...
“Sunlight?”
Yozuki muttered, and we all started running at once. Could the door really have lead outside!?
We were momentarily filled with joy. The door did, in fact, lead outside. But that didn't mean a thing. Because beyond the door was nothing but sheer cliffs shooting up in all directions. We were in the bottom of a very deep hole.
We looked resentfully up at the sky like we were trapped at the bottom of a massive well. We could see the bright blue summer sky, but the cliffs were all obviously too steep to climb, so we could never touch it.
We returned to the underground cave and from there to the mansion, where we once again examined the forbidden door in the backroom, the entrance to the cave. It was said to bring death to any who opened it. We discovered that on the other side – that is, the underground cave side – was another button that opened and closed the door from that side.
“That solves one mystery, at least,” Mitsumura nodded as though she'd understood something. When we all looked at her confused, she explained “There was still an unsolved mystery about the Locked Storehouse, remember?”
“The tunnel that leads into the village was guarded by a gatekeeper, so nobody other than Saboten Iyokawa could have brought the victim, Tabishirou, into the village. But the fact that this sealed door could have been opened from the cavern side means that the culprit could have brought Tabishirou into the mansion through the underground cavern. In other words, there was another route in and out of the village.”
So that was how the culprit had done it. Of course, opening the door would have ripped the talismans, but the culprit could have just prepared a set of replacements and attached them in their place.
With that explained, we went to the entrance of the mansion and out into the garden. We needed to test fire the air rifle used to kill Ryouichirou. Mei had said that when the stake-shaped bullets were fired from the air rifle, the light at the base lit up and a cross-shaped barb emerged from the tip. So we decided to fire the gun and see for ourselves.
Mitsumura loaded the rifle herself. She pulled back the stopper, allowing the gun to gradually fill with air.
Once it was full, the pointed the gun at the ground a bit away from her feet. The ground of the garden wasn't the bare stone floor of the limestone cave, but a layer of black soil. Mitsumura aimed at the packed earth and pulled the trigger. There was a “whoosh”, and the bullet hit the ground five meters away. It moved too fast to see with the naked eye. It probably hadn't broken the speed of sound, but it looked pretty close. It was definitely faster than a crossbow, at least.
We approached where it had impacted. The stake-bullet was buried halfway in the ground. And after being fired from the gun, the light on the base of the stake was glowing green.
“Now, let's see if there's actually a barb at the tip.”
Mei said that and started digging with a shovel she'd prepared. The bullet she removed did have a cross-shaped barb protruding less than five centimeters from the tip.
“I see, it does,” Mitsumura said. “That would make it impossible to stake the victim like a vampire.”
She seemed convinced.
“So there's no doubt that the murder weapon was this gun,” Mitsumura said, looking down at the rifle in her hands. “That means we can narrow down the time of the crime.”
“We can?” I asked. Mitsumura nodded.
“Yes, we can. The gun was unquestionably in the storeroom at 8:00 A.M., correct? And that storeroom is equipped with a security system that operates midnight to 8:00 A.M. The system can't be turned off. Moreover, the device is linked to a siren loud enough to be heard from anywhere in the village. That is, if the door to the storeroom is open at any point between midnight and 8:00 A.M., the siren will sound and everyone will know, preventing the gun from being taken out of the storeroom. So, the gun must have been taken before midnight, ergo, the crime must have been committed before midnight.”
I see, I think. That does narrow down the time of the crime to some extent.
“If that's the case...” said Mei, tracing back her memories. “The gun was definitely in the storeroom at 7:00 P.M., before dinner. Which means the crime must have been committed after 7:00.”
That was true, and I could prove that the gun Mei and the others had seen at that time was the real one. There was absolutely no possibility that the gun they'd seen last night was actually a fake, and that the culprit had hid the real gun somewhere else. That was because when we checked at 8:00 A.M. today, the cuts in the two chains – the one on the surface of the chain attached to the gun and the one on the chain on the wall – had matched. If the two guns, “Gun A” that had been there last night and “Gun B” that was there this morning, were actually different guns, the cuts on the chains wouldn't have matched. Therefore, Gun A and Gun B were the same gun. And since Mitsumura's test fire had just proven that Gun B was the real thing, it followed that Gun A – the one Mei, Yozuki, and Teika had seen in the storeroom last night – was also real.
In short, Mei was right, and Ryouichirou was killed after 7:00 P.M.
“Well, that's all true, but,” Camembert said. “To begin with, Ryouichirou was still alive at 7:00 P.M. We all ate dinner with him.”
“Oh, right,” said Mei.
“Who was the last person to see Ryouichirou alive?”
When Mitsumura asked, everyone looked at each other.
“I don' think anyone saw him after dinner,” Teika answered for the group.
Mitsumura stroked her black hair in thought for a moment. Then she suggested “Can you tell me in detail what everyone did last night?”
“Ah, I'll go get Mr. Chusaita,” Yozuki said, raising her right hand. “He was in the mansion yesterday, too.”
Yozuki said that and ran off towards the Western Village. She returned about 30 minutes later with Chusaita in tow.
And so, they all went over last night's actions.
Mitsumura took everyone into the living room one at a time and questioned them one by one about what they'd done last night. Everyone nodded and discussed last night's events from their own perspectives in as much detail as they could. Mitsumura consolidated their stories into a single timetable.
Timeline of the Night of the Incident
6:50 P.M.: Yozuki, Teika, and Mei confirm the air rifle's presence in the storeroom.
7:00 P.M.: Yozuki, Teika, Mei, and Camembert move to the living room, Ryouichirou and Chusaita start dinner.
8:00 P.M.: Dinner ends, Camembert moves from the living room to the northern section.
8:05 P.M.: Camembert returns to the living room with his guitar case, moves to the southern section.
8:10 P.M.: Ryouichirou moves to his room in the southern section.
8:15 P.M.: Yozuki, Teika, and Mei start assembling Summer Hina dolls.
9:00 P.M.: Yozuki exits the building via the southern section for a night walk.
9:30 P.M.: Yozuki returns to the living room.
10:00 P.M.: Camembert returns to the living room, still holding his guitar case, moves to northern area.
10:05 P.M.: Camembert returns to the living room and helps assemble the Summer Hina dolls.
10:30 P.M.: Chusaita moves to the northern section to use the bathroom.
10:40 P.M.: Chusaita returns to the living room, moves to the southern section intent on returning to the police box.
11:10 P.M.: Chusaita returns to the living room, asks to use bathroom, returns to northern section.
11:20 P.M.: Chusaita returns to the living room.
12:00 A.M.: Chusaita exits mansion via southern section.
12:05 A.M.: Summer Hina dolls are assembled.
12:10 A.M.: Yozuki, Teika, Mei, and Camembert leave the living room.
“Hmm...” Mitsumura was looking over the timeline she'd created. “Miss Teika and Mei never once left the living room.”
“That's right,” said Teika. “Neither of us took a single step out of that room.”
“That is true,” said Mei. “I suppose that's lucky for us. We can give each other alibis.”
Not only that, but their alibis were perfect.
“And there isn't any way of getting to the storeroom in the northern section where the air rifle was kept without passing through the living room... is there?”
Mitsumura said that, then sat thinking for a while. While she was doing that, I asked Yozuki something.
“By the way, Yozuki, you went out for a walk at 9:30. Why were you outside that late?”
“Because I wanted to feel the night air,” she replied. “Girls have nights like that sometimes.”
“No, you were just skipping work,” Mei harshly reprimanded her. “You thought assembling the Summer Hina dolls was too much trouble.”
“No, no, that isn't it!” Yozuki was flailing with panic. “I just wanted a quick change of pace. I wanted to enjoy the night air and listen to the guitar.”
“The guitar?” I asked.
“Yeah, while I was out walking I saw Camembert playing the guitar. It had some sort of cat pattern on it.”
Yozuki recounted what had happened.
“Yeah, that's all true,” said Camembert. “The two of us were out serenading the muses together.”
Serenading the muses? What was with this guy? I was confused, but Mitsumura started speaking as though she'd just realized something.
“If Ryouichirou left the living room at 8:10 P.M., the crime must have been committed between 8:10 and midnight.”
That made sense. But...
“What if everyone was drugged unconscious?” I asked. “Even if the storeroom's security system went off in the middle of the night, no one would have noticed, right?”
“No, I don't think that happened,” said Mitsumura. “Even if they were drugged, an ordinary sleeping pill wouldn't have been able to keep someone asleep through that noise, and any sleeping drug strong enough to keep them all down would have caused them to wake up still fatigued. But that didn't happen, did it?”
They all looked at each other.
“Yeah, I slept fine as ever. Totally normal,” replied Yozuki. “It felt like an ordinary night's sleep. I didn't suddenly get super sleepy or anything, and I woke up feeling refreshed.”
That meant she hadn't been drugged.
“Besides,” Mei said, raising her hand. “Even if we'd been drugged, the siren still would have sounded. You might know this already, but at the village festival, the Yatsuwako Myojin Festival, the village's eight shrine maidens perform a ritual to worship one aspect of Yatsuwako Myojin each day.”
Come to think of it, Okamibara had mentioned that before.
“That ritual takes place from midnight to 8:00 A.M. In other words, it coincidentally takes place at the exact same time the security system for the storeroom is activated. The rituals take place in a series of eight prayer halls scattered throughout Yatsuwako Village, and the eight shrine maidens station themselves in the eight prayer halls and pray continuously for eight hours, without stopping to eat or drink.”
Hearing that, I finally realized what Mei was saying.
“So those eight shrine maidens were definitely awake between midnight last night and eight in the morning?”
“Yes, so if that siren had sounded, at least the eight shrine maidens would have noticed. After all, the siren is loud enough to be heard throughout the entire village, so they couldn't have missed it. And if that siren had gone off at night, it would have caused a commotion. So since there was no commotion, it means the siren didn't go off.”
That was true in theory. But we decided to talk to the eight shrine maidens and get confirmation, so we returned to the Western Village. On the way, we saw a black cat wearing a collar on the side of the road. Yozuki recognized it and said “Oh, that's the same cat I saw the day before yesterday.” But when she reached out to touch it, the black cat dodged her and ran off. The black cat disappeared into a house with an open door, but soon emerged, held in the arms of a young woman in a dress. “How convenient,” said Mei. “She's one of the shrine maidens.”
And so, we went to the homes of each of the shrine maidens one by one, but all eight of them gave the same story. As expected, none of them had heard any siren during the night. However, they had heard the siren when Mitsumura opened the door at 7:50 that morning quite clearly. That meant the prayer halls weren't soundproofed, so if it had gone off that night, it would have certainly reached their ears. I considered the possibility that the prayer halls had been covered with soundproofing sheets, but they also had windows, through which they could see the artificial moon on the ceiling of the limestone cave – the same one Yozuki and I had seen on the night of the festival. We were told that was the same in all eight prayer halls. So if the prayer halls had been covered in soundproofing sheets or some sort of soundproof dome, the moon wouldn't have been visible, and the eight shrine maidens definitely would have realized something was wrong. So it seemed unlikely that the prayer halls had been soundproofed – not that the siren as loud as a space shuttle launch could have been blocked by sheets.
Afterwards, we went to the eight prayer halls scattered around the village, which, like every other building in the village, were boxes painted with plaster. Just as the shrine maidens had said, there were fixed windows in each hall, and through those windows, we could see the artificial moon on the cave ceiling – though it was turned off now.
After we finished investigating the prayer halls, we decided to take another look at the wire mesh over the entrance to the cavern. Mitsumura said she just wanted to be sure. When we did, we found absolutely no signs that any part of the mesh had been cut or torn, and the spear tip on the bottom edge was still lodged in the wood on the ground. If that wire mesh had been raised and reinserted later, there would be a mark in the wood where the spear tip had been pulled out. But we didn't find any traces like that, and by extension, no evidence that the wire fence had been raised. There was no way anyone could have passed through that tunnel.
After confirming all that, we returned to the Eastern Village to investigate the siren itself, but Mei gave us two new pieces of information.
First, the siren was surrounded by a low iron fence, but if anyone climbed over that fence, a sensor would go off and the siren would ring. That meant there was no way the culprit could have approached the siren itself and blocked it off. There was also no way that the speaker had been covered days in advance, then the blockage was retrieved after the crime by pulling on it with a string or something. That's because the siren's speaker was quite large, so if it was covered, the sheet would have had to be equally large. There was no way such a large soundproofing sheet could have been recovered without it triggering the sensor.
The second piece of information was that the siren emitted an infrared beam in five directions, one towards each of the four walls of the cave and one straight up to the ceiling, and if any of the beams were blocked, the siren would ring for the next twenty-four hours. That meant that if, for example, a dome made of soundproof material larger than the siren was placed over the siren, it would block the infrared, and the siren would sound out for the next twenty-four hours. Obviously, that included the morning after the crime, when the dome's presence would have been noticed immediately. That meant there was no way that method had been used, either.
Of course, as I've already said, the unfathomable roar of that siren wasn't something that could be blocked with mere soundproofing material, but this was additional confirmation that such methods hadn't been used.
I nodded and organized my thoughts.
First, Yozuki's testimony confirmed nobody had been drugged. Second, if they weren't drugged, the sound of the siren definitely would have woken them up, so we could confirm that it hadn't gone off. Lastly, the testimony of the eight shrine maidens additionally confirmed that no sirens had sounded.
That settled it: the time of the crime was between 8:00 P.M. and midnight.
And so, we'd managed to narrow down the time of the crime, but there was still much to do. First, Mitsumura and I asked Yozuki about what had happened while we'd been locked in the room with the descending ceiling. Yozuki shared everything she'd seen and heard between 2:00 P.M. yesterday and the early morning of today. However, we didn't get much useful information. Apparently, she'd played shogi all day until dinner, then, after leaving the living room at midnight, she'd taken a bath then gone right to bed. What was important was what happened between 8:00 P.M. and midnight, the time of the crime.
Next, Mitsumura and I decided to head to the scene of the Locked Temple where Saboten Iyokawa had been killed. It was a case made to look like a suicide. There were still two unsolved locked room murders in the village, but Mitsumura had said earlier that she'd already solved this one, so we decided to get it out of the way.
Incidentally, the others had all said they were tired and gone back to their rooms, so for now, Holmes and Watson investigated alone. Mitsumura whined “I'm tired, too,” but I pretended not to hear her.
And so, we went to the Western Village and arrived at the temple-like shrine dedicated to the kazeitachi.
We entered via the window with the now-broken wooden lattice and took another look around the scene. The only entrance to the building was the sliding door, which was boarded up from the inside and couldn't be moved at all. It would have been impossible to nail in the boards from the outside, so there was no way for the culprit to get in or out.
And yet, the culprit had been able to enter and leave the temple. How? I took another look at the spot near the center of the room, where Saboten Iyokawa's body had lain. The body had already been moved to the wine cellar of Ms. Okamibara's inn for preservation yesterday afternoon. So I had to picture the scene as it had been in my mind's eye. Saboten had been clutching a knife in her hand, and at first glance, the scene looked like a suicide. A deep cut was left on her throat by a sharp blade, leaving a pool of dried blood on the floor, 70 cm in diameter. I considered the possibility that the culprit had somehow manipulated the knife from outside the temple and slit the victim's throat. But would it really have been possible to make such a deep clean cut like that? And then to place the knife in her hand...
“No matter how you look at it, that's impossible.”
That's what Mitsumura said. I had to agree. Even if the window had no glass, the mesh on the lattice was so fine that you could barely fit a thread through it. Even if you tried to tie the thread to the handle of the knife and whip it at the victim's throat, it would be hard to hit it accurately, and even harder to get enough power to actually slit the throat.
“So then, how did they do it?”
I had to admit, I was at a loss. Mitsumura shrugged and said “Like I said before, it's an extremely simple trick.” Then, raising her pointer finger, she continued.
“To put it simply, the culprit used a secret passage.”
My eyes went wide, and I reflexively blurted out “That's ridiculous!”
I had to reprimand her after that.
“You really think this temple has a secret passage?”
“What are you talking about, Kuzushiro?” Mitsumura looked at me as though I was the one who'd said something ridiculous. “There's no way such a simple temple could have a secret passage. I've been wondering this for a while now, but are you an idiot, Kuzushiro?”
Where did this bitch get off!? She was the one who brought up secret passages to begin with! I was really mad. The injustice of it all turned my stomach.
The “this bitch” in question just shrugged her shoulders.
“Don't get mad at me because of your misunderstandings,” she said, stroking her black hair with long, slender fingertips. “I never once said this temple had a secret passage. The culprit built one themself and escaped through it.”
The culprit made a secret passage? I took a shocked look around the room.
Mitsumura completely ignored me and said “I'll prove it now,” then left the temple via the window. “I have to get some tools.”
About ten minutes later, she returned and, after leaving something outside the window, stepped back inside.
“Well then, shall we begin the deduction show now?”
Mitsumura showily swung her hand around to her chin.
“As I've said several times now, this trick is extremely simple. The culprit made a secret passage. Which is to say, they made a hole in the wall or floor large enough for them to pass through, and escaped through it.”
I frowned at her explanation and took another look around the room. Of course, the problem with her claim was obvious. There weren't any holes in the room large enough for a person to pass through.
“To start with,” I said, “isn't that theory completely unreasonable? This temple is made of wood. If a hole large enough for a person to pass through were drilled in a wooden wall or floor, it would be extremely obvious. At that point, the trick wouldn't work anymore-”
“So they hid the hole – How they did that is the most important part of the trick.”
Hiding the hole they drilled to escape – In other words, the hole was still here in the temple, and the culprit had cleverly hidden it.
But where?
“For example,” said Mitsumura, “Suppose the culprit drilled a hole in the wall, sealed it up, then painted over the traces left behind. Then, when the paint dried, it would completely hide the traces that there had once been a hole there. What if the same thing happened in this room?”
“So the culprit painted over the hole they used to escape?”
I took another look around the room, but there weren't any traces of paint anywhere. So I looked back to Mitsumura, who silently pointed to the floor in the center of the temple and said “Over there.” There was a pool of blood with a 70 cm diameter there, right next to where the body had been.
“No.”
“Yes,” Mitsumura nodded. “The culprit made a hole right there in the center of the room and jumped down. The blood that spilled from the victim's neck created a pool of blood right over top of it, eventually coagulating to the thickness of paint, completely covering any traces of the secret passage the culprit made.”
When I heard Mitsumura's theory, I looked back at the pool of blood in the center of the room. The floor's surface was completely covered reddish-black dried blood. It didn't look like there was a hole big enough for a person to pass through.
“Well, let's see about that.”
Mitsumura leaned out the window and retrieved the thing she'd left outside the temple. It was a bucket of water and a deck brush. Mitsumura dipped the deck brush in the water, then started scrubbing the pool of blood in the center of the room. The blood flowed away, revealing the floor hidden beneath. There was a clear trace where a circular hole had been made. It looked like it had been hollowed out and then put back.
“I believe you observed this during our first investigation,” said Mitsumura, “but the floor of this temple is slightly inclined towards its center. So, the blood that spilled from the victim's throat eventually pooled in the center of the room. And because the blood pooled in that one spot, it formed quite a thick layer. When it dried like that, it completely hid the hole in the floor, just like this.”
I nodded in agreement. It all made sense, logically. But then, I suddenly noticed a major flaw.
“There's no way a proper police investigation would miss this.”
I mean, there's a huge hole in the middle of the scene. Even if the police didn't notice it, once the blood was washed up after the body was removed, it would be right there in plain view. It was only a matter of time before this trick was exposed.
“Yes, that's why they made this village a closed circle,” Mitsumura said, playing with the end of her hair. “This trick can only be performed in a closed circle, where the police can't investigate. That's why I believe the culprit is planning to burn down this temple before the police arrive. If they did that, the hole in the floor would also be destroyed. That would destroy all evidence of this trick, wouldn't it?”
It would. However, it would have been too obvious to burn it down right away, so the culprit was probably waiting as long as they possibly could. That was another sign of the culprit's confidence in this trick. They were sure nobody would realize the truth, even with this large hole right there in the floor. And that wasn't necessarily overconfidence. Although it was a simple trick, it had managed to completely sucker in Mitsumura for a while, and although it wasn't exactly invisible, there was no doubt that a pool of blood at a crime scene wouldn't raise many eyebrows.
And so, the sixth locked room, the Locked Temple, was solved, and with it, we proved that Saboten Iyokawa had been murdered. The next thing Mitsumura and I did was to investigate the seventh locked room, the Locked Room of Four Color Boxes beneath the Monokaki Family's mansion. Kyoujirou's body had also been moved to a wine cellar, in this case the one there in the mansion.
The Locked Room of Four Color Boxes was a simple concrete building. The floor was wood and the inside walls had white wallpaper.
The room was filled with colorful wooden boxes. The boxes were of various sizes, but were uniformly of about waist height. And those boxes were barricading the inward-opening door, keeping it from opening. The wooden boxes placed in front of the door were much wider than the doorway itself.
So, once again, I had to ask.
“How did the culprit block the door?”
The wooden boxes were packed into the room like sardines, barely a gap to be seen. The only space in the room without any boxes was the southeast corner of the room, where the body had been. So Mitsumura and I started by shifting the boxes towards the southeast corner one by one. That is, we slid the box next to the empty space into the southeast corner, then moved the adjacent box into the new empty space we'd just created and so on, like a sliding puzzle. It was pretty tedious, but moving the boxes one at a time like that was the only way to move the box blocking the door.
We kept working like that, and eventually, we were able to “move” the empty space in the southeast corner in front of the door. We'd had to move eight boxes to do it. Now we could open the door. This must have been how the boxes were arranged when the body was brought into the room.
To block the door with the wooden boxes, you had to do the opposite – slide the wooden boxes back to the space in front of the door and move the space to the southeast corner. Then the door would be blocked by the boxes and couldn't be opened. By following those steps, the Locked Room of Four Color Boxes could be recreated.
The problem was...
“We need to do all that from outside the room.”
With the wooden boxes blocking the door, we couldn't get into the room, obviously. So the culprit must have moved the boxes from the outside. But how?
“There isn't any gap under the door, either.”
I peered under the door and said that. So there was no way to move the boxes towards the door using a string under the gap.
So, what we did have to work with was...
“The water and the round stones in the boxes.”
I opened the lid of a wooden box, just like I had during our previous investigation. The inside of the boxes were shaped like sake cups, and had surprisingly little open space. Just as it had been before, this one was filled with water and a stone the size of a softball.
Mitsumura removed the lid from another box, looked inside, and said “Shall we split up and open all the boxes again?”
And so, Mitsumura and I once again opened all the boxes' lids. Of course, nothing had changed since the last time we checked: all of the boxes contained water, and eight of them contained stones. But, although I hadn't thought anything of it earlier, I realized that eight was an important number here. In order to create the locked room, you needed to move eight boxes like a sliding puzzle. The stones were in those same eight boxes.
“Hmm, I see,” Mitsumura said thoughtfully. “And looking closely, the amount of water in each of the boxes is different.”
When she said that, I looked in each of the boxes again. All of the boxes containing stones were the same size, but the amount of water in each one was definitely different. When I tilted my head to the side, Mitsumura spoke.
“Kuzushiro, do you have anything to write with?”
“Huh? Oh, here.”
I handed Mitsumura a pen and my notepad. There, Mitsumura drew a diagram of the current layout of the wooden boxes in the room. Then, she labeled the eight boxes containing stones A through H, in order of how close they were to the door.
Mitsumura ripped it from the pad, showed it to me, and said
“See? The closer to Box A a box is, the less water it contains.”
“Huh.”
I saw that, but I wondered why it mattered.
But then Mitsumura said “Maybe...”, shifted the boxes a bit, went “Hmm...”, then tilted one of the boxes to one side. When she looked under the box, she laughed. “I knew it.”
“Just as I expected.”
“Huh? What is?”
I looked under the box Mitsumura was tilting over and saw a small space. The edge of the box's bottom protruded about 10 cm further than the rest of the box, creating a small space between the box and the floor. However, the edge of the box was completely flush with the floor, making it impossible to see the space without lifting the box and looking from below.
I tilted my head a bit, then Mitsumura handed me my notepad back and I drew a quite schematic of the box itself. I scratched my head as I looked at it.
“But what does this mean?”
Why was there a space under the box? I had no idea.
But Mitsumura looked confident.
“Alright then, I'll tell you.”
My eyes went wide at her words.
“So, does that mean...?”
“Yes,” she said, stroking her black hair. “The mystery of this locked room has been solved.”
“I'll show you how to do it,” Mitsumura said before leaving the room. She took one of the stones from the boxes as she went. How mysterious. Left alone in the room, I sat down on one of the boxes and felt bored.
Thirty minutes later, Mitsumura returned. She'd brought Yozuki with her, and the two of them were carrying something big. It was a stove full of charcoal used for camping. Apparently, Mitsumura had called Yozuki to help her.
“Phew, that thing's heavy,” Yozuki said after setting down the stove. “I've been sentenced to hard labor.”
“Thank you for all your hard work,” Mitsumura said as she wiped the sweat from her brow.
The charcoal in the stove was already red hot. And on top of the charcoal was the stone Mitsumura had taken earlier – the round one taken from the water in the wooden box. The stone was being heated by the charcoal and was itself changing color. What were they-
“Well, shall we begin?”
Mitsumura entered the room and opened the lid of the wooden box closest to the door. That box had been moved away from the door, leaving a space for the door to open.
“All we really need to do to seal this room is to move this box into this open space,” Mitsumura said. “Of course, in reality the culprit moved eight boxes, but is it okay if we only move one for the demonstration?”
I nodded at Mitsumura. The question was how she was going to move it.
“All we need is the water and this stone,” Mitsumura said, pointing to the things in the box. “However, we're going to use the stone over there, so we don't need this one.”
Mitsumura removed the stone from the box. Then she turned to the charcoal burning outside the room. The stone on top of the stove was red hot. So, the trick required a hot stove.
“Yes, just like the one the culprit used. Well, Yozuki, if you will.”
Perhaps Yozuki had been briefed beforehand, as she said “Okay” without a moment's hesitation. Then she picked up a pair of tongs hanging from the stove and used them to pick up the hot stone. She carried the stone with unsteady hands and dropped it in the water in the box closest to the door. It instantly released a large amount of steam. Yozuki ignored it and closed the lid of the box, then the door. Then she looked at Mitsumura with an irritating smugness. Mitsumura gave her a thumbs up. I'm glad my friends are friends with each other.
“And now we're ready,” Mitsumura declared. “All we need to do now is wait for the box to move.”
Wait, what? Wait for the box to move? What was going to move the box?
“It's obvious,” Mitsumura laughed. “I'm going to push it by hand.”
Obviously, she was joking.
“Decide whether it's a joke or not after you see the results. It shouldn't be long now.”
Mitsumura looked at the wooden box the hot stone had been placed in. Yozuki and I watched with bated breath. And then, after about a minute, it happened.
The wooden box closest to the door suddenly started to move, as though someone was pushing it. It moved smoothly across the floor, as though it were floating. Then it hit the door and stopped. The wooden box had slid right into the space in front of the door, and was now completely blocking it. I was stunned.
“How on Earth did you do that?”
Mitsumura scoffed.
“I pushed it, of course.”
No, you clearly didn't.
“Sorry, I got a bit carried away.” At least she sounded like she was reflecting on her actions. After giving a cough, she said “This trick makes use of a certain phenomenon.”
“A certain phenomenon?”
“Yeah, I don't know if it has a proper name,” said Mitsumura. She raised her index finger. “I only know it as 'the phenomenon that makes miso soup move on its own after its placed on the table'.”
Even with how bizarre the trick she'd demonstrated was, her explanation was still a shock. I did know about the phenomenon she'd described. The strange phenomenon where bowls of miso soup would move on their own.
“The culprit used that phenomenon to create a locked room,” said Mitsumura. “You see, there's an open space between the bottom of a miso soup bowl and the table. When you pour hot miso soup in the bowl, that heat causes the air beneath the bowl to expand, lifting the bowl enough that its friction becomes almost zero. Then, if the table its kept on has even the slightest incline, in slides down. That is the scientific basis behind that phenomenon.”
Yozuki's eyes shot wide open, and she breathed a statement of disbelief.
“Is that what it is? I always thought it was a ghost.”
Of course she did.
Granted, I hadn't known why that phenomenon happened, either.
“So that's why the wooden boxes moved.”
“Yes, exactly it,” Mitsumura nodded. “The wooden box was filled with water, and when the hot stone was put in, the water started boiling. That caused the air beneath the box to expand, causing the box to rise like a bowl of miso soup.”
I see, I think. So that's why there was a space between the bottom of the boxes and the floor. Come to think of it, I the shape of the boxes' insides was similar to a bowl. No, they were clearly modeled after bowls on purpose.
“But to make the boxes float, the bottom of the box needs to be firmly in contact with the floor, so they sprinkled a small amount of water around the room beforehand. That caused the boxes to grip the floor more tightly. You know how when you put a bowl on a table, a bowl with a wet bottom will stick to the table better than one with a dry bottom? It's the same principle. And the floor of this room...”
Mitsumura looked down.
“It must have an incline too subtle for us to notice. So, the boxes lifted by expanding air slid along that invisible slope and moved as if by magic. Furthermore, as you can clearly see, the entire room is packed full of boxes, so the moving boxes were blocked on both sides by other boxes. The static boxes formed a path, so to speak. The box that started moving went straight towards the door as though it were on rails. The centers of gravity and weights of the boxes must have been carefully calculated to ensure they'd go down the slope properly, as well. After all, these boxes were made by the all-purpose genius Zerohiko Monokaki based on an idea from one of the Eight Locked Room Masters of the Showa Era, all for the sole purpose of creating a locked room. They aren't just any wooden boxes. They must have been carefully constructed to ensure that they could be used for this trick a hundred times and produce a hundred successes.”
So no matter how many times the culprit tried, the locked room would have been created with 100% certainty. So, all that remained to be answered was...
“How did they move the remaining boxes?”
There was more than one box that needed to be moved. By moving one box, the space in front of the door had been moved south by the width of one box. However, to complete the locked room, the other boxes needed to be moved in the correct order like a sliding puzzle, eventually moving the space to the southeast corner. Since the boxes moved along the slope of the floor, it made sense if the path they moved along was deliberately installed, and they moved towards the door automatically. The problem was that if the hot stones that powered their movements were placed in all the boxes, they'd all move at once and bump into each other. Wouldn't that mean they couldn't assemble the locked room? Therefore, the culprit had to move the boxes one at a time.
“Yes, you're right,” said Mitsumura. “That's why the culprit changed the amount of water in each box.”
Saying that, she took a folded piece of paper from her pocket. It was the diagram of the wooden boxes she'd drawn earlier. The boxes were labeled A to H, in increasing order of the amount of water they contained. Box A contained the least water, and Box H, the most. The box closest to the door was labeled A, and the box furthest from the door was H. That meant the boxes we wanted to move later contained more water.
“Which means...”
“It's as you suspect,” Mitsumura nodded at me. “The less water there is, the faster it boils. And the faster it boils, the sooner the air beneath the box will heat up. So the boxes will move in the order of least amount to water to most – the same as alphabetical order as written on this diagram. So even if the stones are all put in at almost the same time, the boxes won't move at the same time, but will move one by one in a regular order. And as a result, the empty space will move slowly but surely away from the door and eventually come to rest in the southeast corner.”
Which was exactly where we'd found it when we discovered the body. That was how the Locked Room of Four Color Boxes was created.
With the Locked Room of Four Color Boxes solved, we went back upstairs and returned to the surface. I bumped into Mei at the top of the stairs. Teika and Camembert were with her.
“Oh, Mr. Kuzushiro and Miss Mitsumura, you were here?”
It seemed they'd been looking for us. I asked “What's up?”, and Mei apologetically replied “We realized there was something we forgot to tell you.”
“The underground maze where Ryouichirou's body was found... There's actually a security camera there.”
We all went through the underground maze to the room where Ryouichirou's body was found. Halfway through the maze, Mei stopped and told us “Look, there it is. There's the security camera.”
Looking over, we saw that there was indeed a security camera there.
According to what I'd heard from Camembert before, this basement was a huge underground space with concrete walls in the shape of a flat-sided rectangle like a box of cookies. The space was divided up with metal walls painted black, creating an enormous maze of metal and concrete. The security camera was set on a tripod that was fixed to the concrete at my feet with screws. The camera was about the size of a smartphone, and was set to face due east. The camera's back was to a metal wall, so close that there wasn't any gap between the wall and the camera.
“I forgot to mention it earlier,” Mei said, looking embarrassed. “It's been a while since I was last down here.”
The passage was wide enough that we hadn't noticed the camera when we passed by it earlier.
“Huh? But if the camera's positioned here...” Camembert said, tilting his head. “Maybe the image of the one who killed Ryouichirou was caught on camera.”
“There's no way.” Teika sounded exasperated. “They must've hid their face, right? The culprit ain't stupid.”
I certainly doubted it would be that easy.
“But we should still check, just in case.”
When I said that, the others all agreed.
Apparently, the security camera's footage could be viewed on the computer. So we went back above ground and went to the room in the mansion where the computer was kept.
“But before that,” Mei said as she sat down in the computer chair. Then she brought up an image on the monitor. “This is a map of the underground maze.”
We all looked at the map. The map included the locations of the security cameras, of which there were five in total. And all five of those cameras were watching spaces on the path to the room where Ryouichirou's body was found. Which is to say, it was impossible to get to the scene without passing in front of all five security cameras.
“Alright, now let's check the footage.”
Mei opened the security cameras' footage and hit play. After a while, her eyes opened a bit wider.
“Huh? That's strange. There's no one there.”
Indeed, not a single soul appeared in any of the five feeds. The only time any of the images changed was when Mitsumura and I passed by at about 7:20 that morning, when we discovered the body. Then we appeared, hurrying back to call the others, after which the whole group passed by about ten minutes later.
But neither the culprit nor the victim, Ryouichirou, appeared in the footage at all. From 8:00 P.M., when Ryouichirou left the living room, to 7:20 A.M. the next morning, when Mitsumura and I found the body, the cameras showed nothing but empty passages.
It was a situation where not only the culprit but even the victim couldn't go to the crime scene. This was exactly...
“It's a locked room,” Mitsumura said, running her fingers through her black hair. “I suppose this would be the Locked Underground Maze?”
Locked Room Draft No. 5 (By one of the Eight Locked Room Masters of the Showa Era: Ouki Tatsuda)
The victim's body is discovered in a massive indoor maze. Inside the maze, several guards sitting on metal chairs are posted, but the culprit is able to make their way through the maze without being seen by any of them.
With that, all eight of the final tricks left behind by the Eight Locked Room Masters of the Showa Era had been used. Which meant that Zerohiko Monokaki's murder plot – the plot to committed the eight locked room drafts in real life – had been completed.
The locked room situation depicted in Locked Room Draft No. 5 was nearly identical to the Locked Underground Maze where Ryouichirou had been killed. The only difference was that the guards sitting in metal chairs had been replaced with security cameras mounted on tripods.
Afterwards, Mitsumura and I decided to visit the underground maze and solve Locked Room Draft No. 5 – that is the Locked Underground Maze.
“First, we need to confirm that this map is accurate.”
Mitsumura was holding a printout of the map of the underground maze, which Mei had given us. We passed through the maze, verifying that it was correct. First, we checked the positions of each of the security cameras in the maze. They were all in the same positions as they were on the map.
All five cameras were fixed to the concrete with tripods, and all of them had lenses facing either straight east or straight west. The directions each camera faced were also written on the map, and the descriptions and the actual directions of the lenses also matched. In addition, all of the cameras had their backs pressed to the metal walls, without any gaps between the walls and the cameras. That meant there was no way to slip behind the cameras. They were cameras without any blind spots.
Next, we checked to see if there were any gaps in the walls themselves. Or whether there were any parts of the metal walls that opened. And our findings confirmed that that the metal walls were all securely connected; there were no gaps . It was impossible to go any way other than the designated route. And, of course, there were no secret doors in any of the walls. The maze had no secret passages.
So the map was accurate, after all. That meant the crime scene was a perfect locked room... At least, that was how things looked.
“Yes, it's too impossible,” Mitsumura said, putting her hand to her chin. “It's impossible to get past one security camera, let alone five.”
The locked room had five security cameras. It was unquestionably impossible to enter or leave the crime scene without being caught on any of them.
Or so I thought. But...
“Can I get serious for a second?”
Mitsumura thought differently, and took a hair tie from her pocket. She tied her hair back in a ponytail. When he had her hair in a ponytail, she could concentrate better. I had only learned about that special ability yesterday.
When she tied back her long black hair, the light behind her eyes went out. Her once cool eyes turned sharp and pitiless. They were the eyes of a murderer.
“I'll start working now. Just be quiet for a moment.”
Mitsumura put her right hand under her jaw and stared intently forward. But nothing was reflected in her eyes. All she could see was the past. She was sifting through the clues hidden in her memory and using them to reconstruct the path to break down this locked room.
And after seventeen seconds, she undid her hair. The warmth returned to her eyes. Though they were still below average in warmth and friendliness.
I saw my reflection in her eyes as she said “I've got it.”
They were the words she spoke when a locked room was broken. When I reflexively asked “Really?”, she laughed and said “Of course.”
And then she declared “Let's just do it now. Let's solve the mystery of the final locked room of the Yatsuwako Village Octuple Locked Room Murder Case.”