Mitsumura had gathered us all in the room where Ryouichirou's body had been found to demonstrate the solution to the Locked Underground Maze. Aside from myself, Yozuki, Camembert, Teika, Mei, and Chusaita were all there. Everyone involved in the incident and still alive was accounted for. But Mitsumura, the most important person, hadn't arrived yet. We wandered the room, waiting, but it took an hour before Mitsumura suddenly appeared before us.
“So sorry to keep you waiting.”
This wasn't something that could be resolved with a “sorry to keep you waiting.” I tried to protest, but Mitsumura put her hands together and kept going “Sorry, sorry.”
“I was looking for something. I thought it would be easy to find, but it took longer than I thought.”
“Looking for something?”
Well now I was curious.
“Well, look forward to it, then.” Mitsumura laughed before taking the watch off of her left wrist and placing it on the floor.
“So, the premise of this locked room trick is that the culprit went to this room and left Ryouichirou's body here without being seen on any of the security cameras in this underground maze, then escaped the maze, also without being seen by any of the cameras. So, I will now demonstrate how that can be done. That is, I will enter this room without being seen on any of the five cameras, retrieve my watch from off the floor, then escape the underground maze, still without appearing on camera. If I can do that, it will mean I've successfully recreated the locked room trick, right?”
We all looked at each other. Without a word, everyone nodded.
If she could enter and exit this room without being seen on the cameras, she would have managed to recreate the trick. And as proof that she had actually entered the room, she was going to retrieve the watch she'd just left on the floor.
“Is that really possible?” Teika asked suspiciously. “No matter how ya look at it, it doesn't seem possible to avoid five security cameras.”
“Oh, but it is possible,” Mitsumura said with a small chuckle. “Well, I'll give you some time to try and figure out how while you're away.”
“Away?” I asked.
“You're going to the room with the computer where you can monitor the cameras,” said Mitsumura. “I want you to watch the cameras in real time and confirm that I really wasn't caught on them.”
“Well, goodbye, everyone.”
As soon as we arrived in the computer room, Mitsumura waved and headed back to the underground maze by herself.
“Well, let's see what there is to see,” said Mei.
The footage had already been pulled up on the computer. Five windows were open on the screen, showing real time footage of the underground maze.
So, we stared at them. We all concentrated hard, sharpening our senses to the point where nobody would have missed a mouse scurrying by. The clock on the wall ticked away. Ten minutes passed. Twenty. Thirty... Finally, after an hour,
“Not yet?” Yozuki said, finally running out of patience. “Mitsumura still hasn't gone by?”
Nobody had appeared on the camera. Well, Mitsumura had said that she was going to slip past the camera's surveillance, so it was better if she didn't appear on the feed. But even so, she'd been gone an hour. She was taking too long.
Teika said “Maybe Mitsumura's waiting for us to lose focus.”
“You mean...?”
“Yep, that's right, Kasumi. That's Mitsumura's plan. She's waitin' for us to stop focusin' on the camera feed an' look away so she can slip by through the passages bein' monitored by the cameras.”
That was a dirty trick.
“Wait, that can't be it,” I said defensively. “She wouldn't do something like that.”
“If it's Mitsumura, she totally would,” said Yozuki. Just what sort of person did she think Mitsumura was?
Just in case, we stared at the monitor even harder. An hour passed, then another, and finally, a full three hours after she'd left, Mitsumura returned.
“Sorry keep you waiting.”
Seriously?
“I wish you'd warned us you'd be gone that long.”
When I criticized her behavior, Mitsumura nonchalantly said “Come to think of it, I forgot to mention.”
“This trick takes a very long time.”
Thanks to that, we were all completely exhausted. It was only natural, seeing as how we'd been staring intensely at a computer screen for three hours straight. We all glared at Mitsumura with eyes full of resentment. Mitsumura groaned and said “I suppose I was also at fault,” but then immediately went “But!”
“I got us our results. Look.”
She showed us the object in her hands. At that moment, all of our fatigue evaporated. We stared at it in disbelief.
It was a wristwatch. The same one she'd left behind in the room in the underground maze earlier.
“So,” I gasped, “you managed to sneak into the underground maze and retrieve the watch?”
“That's impossible!” Mei shouted. “Nobody appeared on the cameras!”
That was true. We'd monitored all five cameras in real time. But there had been no sign of Mitsumura, or anyone else, either. So how had she been able to get through the underground maze?
Teika suggested “Maybe we just missed her? So Mitsumura did appear on camera, but we all just so happened to miss her, and as a result, the locked room was created by chance?”
“Is that really possible?” asked Camembert. “There were six people monitoring the cameras. You really think we just so happened to all miss her? Five times in a row?”
Five cameras did meant that Mitsumura had appeared in the footage five times. No, she had to go there and back, so it was ten times. It was hard to imagine every single one of us missed her ten times.
So Mitsumura had genuinely slipped past them. She used some trick to avoid all five security cameras.
“But how?”
I blurted out my honest feelings. Mitsumura smiled.
“I'll tell you, of course. A detective who doesn't reveal her secrets is no different than a stage magician.”
“Well, let's begin the explanation.”
Mitsumura took out a folded map of the underground maze and stuck it to the wall with clear tape, then stood next to it.
“Just to review, this is the structure of the underground maze where the incident took place. As you can see, the only route to the scene of the crime is monitored by five cameras. So, how did the culprit and I get there? To find that, you need a change in perspective.”
“A change in perspective?” asked Yozuki.
“Yes, and I mean that completely literally. You need to change the way you look at the maze. For example,” Mitsumura asked, turning to me. “What does this map look like to you, Kuzushiro?”
“What does it look like?”
I was confused by the question. What does it look like? That didn't matter-
“No, it doesn't,” Mitsumura nodded. “But what if I make a few changes? For example... These?”
Mitsumura took out a felt tip pen and added some black lines to the map (see following image), then smiled and said:
“How about it? Has this changed your perspective?”
Our eyes had all shot open. Before, it had looked like a view of the maze from above, but Mitsumura's pen stroke had literally changed our perspective.
The map that had once been a view from straight above was now a side view, like a map of a Super Mario Bros. stage.
So, what we had foolishly assumed was a map draw from above was actually a side view map...
Not.
“W-What?” Yozuki said in shock. “Why are you explaining something so obvious, Mitsumura?”
Indeed, this wasn't news to us. From the beginning, it had been obvious to us that the map was of a side view and not a view from above. For some reason, Mitsumura had explained something extremely obvious. To be honest, I had no idea what she was doing.
“Well, there's no other way, is there?” Mitsumura shrugged. “This map is terrible. Since we've actually been underground, we know that this is a side view map, but if someone who'd never been to the basement were to see it, they would definitely assume it was drawn from above.”
I guessed that was true. If someone who didn't know anything else were to see this map, they would definitely assume it was as seen from above. Mystery fans, in particular, are trained to assume any map they see is a floor plan.
Then there was Locked Room Draft No. 5. It said “Inside the maze, several guards sitting on metal chairs are posted,” which also planted the false notion that the maze was flat. If you were shown a map of the underground maze after reading that draft, it would be extremely difficult to perceive the map as a side view.
“Okay,” said Teika, “but so what? I get that some people might mistake that map for a top-down view, but who cares? Do ya mean to say that viewing the map from the side will help solve the locked room?”
Mitsumura gave a soft giggle and said “That's a good question.” She stroked her black hair before saying “Yes, you're completely right. Recognizing that map as a side view changes one thing dramatically. To be precise, a certain incident that occurred in the underground maze is turned completely on its head.”
“A certain incident?” asked Yozuki.
“Yes, and I'm not talking about the one where Ryouichirou was killed,” said Mitsumura. “I didn't mean to hide it from you all, but yesterday, there was another serious incident in that underground maze. Specifically, a murder attempt. Well, I'm actually not convinced there was a serious attempt to murder anyone, but people did almost die. Two people, to be precise.”
“What!?” I said in shock. “I can't believe something like that happened.”
“What are you talking about, Kuzushiro?” Mitsumura asked, shooting me a scornful look. “You must know about the incident.”
“No, I really don't.” I had no idea what she was talking about.
“Yes, you do,” Mitsumura said stubbornly. Then she sighed deeply and said “Because the two people who were almost killed were you and I.”
“Eh?”
“We were, weren't we? Yesterday, in the room where Fuichirou's body was found, we were nearly crushed under the descending ceiling.”
I gasped. Now that she mentioned it, that was true. We had narrowly escaped death.
But that incident didn't have anything to do with this locked room trick as far as I could see. Until I thought about how the underground maze's map was drawn from the side rather than above, and things started looking different. Because the room where we were nearly crushed beneath the descending ceiling – the room where Fuichirou's body was found – would have been at the far south if the map were drawn from above, but since it was a side view, it was actually at the bottom, deepest underground. In that case, the ceiling that had nearly crushed Mitsumura and I must have also been one of the metal walls of the maze. The underground maze was structured as a huge concrete space separated by metal walls, and the bottom of one of those walls was the top of the descending ceiling.
“And all of the metal walls are connected together,” Mitsumura said. “There isn't a single gap in any of the walls – Kuzushiro and I have already confirmed that. So, what will happen if the descending ceiling is lowered like this? It's obvious. The descending ceiling is the bottom of a metal wall, so if it descends, that means all of the metal walls will descend, and...”
Mitsumura took out another piece of paper from her pocket and pasted it next to the map of the underground maze. It was a new, hand-drawn map of the underground maze, largely the same as the original. But the one difference was staggering.
The entirety of the series of metal walls that made up the maze had been lowered. And when the bottom of the wall hit the ground, crushing the room below beneath the descending ceiling, what happened?
“The cameras' positions changed?”
Teika's voice was barely audible. As she'd said, the position of the cameras had changed relative to the rest of the maze. The underground maze was made by dividing up a huge concrete space with metal walls, and the cameras were all fixed to the concrete with tripods. In other words, the cameras were affixed to the concrete, not the moving metal walls, so when the metal walls moved, the cameras stayed in place. But the entire maze, which was made of the metal walls, had changed. So even though the cameras themselves were fixed in place, the maze was moving around them, which had the same effect as if the cameras had moved through the maze. Which meant the part of the maze the cameras captured had also changed.
“No way...” Mei said, staring at the map of the maze after being moved. “How is that possible?”
Mei stared at the map in confusion for a while, but finally pointed out the end result.
“The path to the crime scene is clear?”
I finally realized the truth. She was right. They were all gone. The route from the entrance of the maze to the crime scene was 100% security camera-free.
Because they'd all been moved out of the way.
“It's because the relative positions of the cameras changed,” Teika said. “The cameras themselves haven't moved, but because all of the metal walls moved, the security cameras' relative positions are higher. As a result, the cameras' views have also moved up, and instead of filmin' the path to the other end of the maze, now they're filmin' completely different parts – nothin' but a series of dead ends.”
As a result, the underground maze blocked by cameras was transformed into an underground maze not blocked by cameras. That made it possible to come and go from the crime scene without being seen at all. Which meant the locked room had been destroyed.
“But,” said Yozuki, “when the metal walls moved, the cameras should have recorded them. But I didn't notice that at all.”
Indeed, when Mitsumura went through the underground maze to demonstrate the trick earlier, we'd been watching the cameras on the computer screen the whole time. If Mitsumura had moved the metal walls, we would have seen it. And even if we'd missed it, it would still be visible when we went back and watched the recorded footage later. So wasn't it impossible for her to have moved the wall without us noticing?
“That isn't even difficult,” said Mitsumura with a proud look on her face. “You already know, Kuzushiro. That descending ceiling moves extremely slowly, doesn't it?”
“Descending slowly...”
I thought about it for a moment, then eventually nodded. Indeed, that ceiling had descended extremely slowly. So slowly that it had taken us a while to notice.
I understood what Mitsumura was getting at. That meant...
“The walls were moving so slowly we couldn't see them?”
The descending ceiling was part of the walls dividing the basement into a maze, so naturally, the walls and the ceiling moved at the same speed. And if a thing is moving too slowly, it becomes impossible for humans to perceive the change. You see it on TV quiz shows: the picture changes extremely slowly, and a majority of people can't even perceive the changes. Moreover, the metal walls were all painted solid black. Even if they moved, the image that appeared on the camera would be the same. It would look identical to a static image of the wall. That was how it could be moved without anyone noticing.
With that new information in mind, it made sense why Mitsumura had taken three hours to demonstrate the trick. We had wondered about that, but now it was clear. That was how long it took for the walls to move out of the way.
“What's more,” said Mitsumura as she turned back to the map of the underground maze, “As you can see on the map, all of the security cameras face either east or west. And importantly, they are all installed below T-junctions, with their backs to the branches of the T-junctions. There's a reason for that. If the cameras faced the branches of the paths, then when the cameras moved relative to the other path, they would pass through their fields of view, right? And if that was captured, the image would change, making it obvious that the walls had moved. That was why the cameras were all installed with their backs to the branches: so they'd only capture walls. As long as the cameras faced walls, there was no change in their images.”
I see, so the underground maze was constructed so that even the camera's orientations would support the locked room trick.
After hearing the explanation, I realized something else. When Mitsumura and I were almost crushed beneath the descending ceiling, I'd assumed the culprit had been trying to kill us. But that assumption was wrong. The culprit hadn't been trying to kill us. They'd just planned to commit the crime that night, so they'd lowered the ceiling during the day because it took so long to descend. Mitsumura and I just so happened to get caught up in it. Our near-flattening was a total coincidence. The reason the descending ceiling was raised the following morning was because the culprit had delivered Ryouichirou's body and completed the crime. They hadn't been trying to kill us, and they hadn't been trying to save us. Thinking about it, it was a bit scary.
But we had been saved in the end. Because of the hidden space Mitsumura had found beneath the room. Looking at the map, the hidden space was properly marked. It was outlined quite boldly.
“So if Kuzushiro or I had been allowed to look at this map beforehand,” Mitsumura sighed, “We wouldn't have had such a scare.”
Afterwards, we went back into the underground maze to see how the cameras were affected for ourselves. We opened up the trap door to the underground maze on the floor of the archive and saw the metal ladder leading down to the basement. As we've established, the underground maze is laid out like a stage in a side-scroller, so you need a ladder to move vertically. The ladder was fixed to the concrete wall, and partway down, a passage moving east appeared. In other words, there was a branching path. If you kept going straight down, you'd arrive in the room with the descending ceiling. The door to that room only opened a maximum of about 70 degrees, so it would fall closed as soon as you let go. There was a rope ladder hanging from the ceiling next to the door, which could be used to descend to the floor. If there had been a metal ladder, it would have been bent when the ceiling descended, but a rope ladder didn't have that problem.
All that said, we weren't going to the room with the descending ceiling right now. So we climbed off the ladder and went down the east passage. The passage continued to the right of the maze, with a metal floor and ceiling. We continued down it until we arrived at a T-junction where the path split into two directions, with a metal ladder going up and down. However, this ladder wasn't fixed to the concrete, but to the metal walls that formed our passageway's floor and ceiling. When we climbed up the ladder, we eventually passed a security camera. The camera was on a tripod, fixed to the concrete wall at my feet. Of course, “at my feet” was a relative term in this context; that just so happened to be where it was at the moment.
The ladder was right in front of the camera, angled so that the rungs were completely hidden by the pole facing the lens. That was important, because since the ladder was fixed to the metal walls, it would obviously move when the walls moved, but the rungs being hidden from the cameras meant it couldn't see their movement. If the rungs had been even slightly visible, it would have been easy to see the ladder's movement, but since we could only see the pole, it looked like a static image. The positions of the ladder and the camera were clearly deliberate, and we could assume that all of the ladders visible to the cameras were set up at similar angles.
So we made our way through the maze, climbing up and down ladders, and eventually arrived to the room where Ryouichirou's body had been found. We'd confirmed that, with the walls lowered as they were now, we could get there without passing a single security camera.
“So all that's left to learn,” said Teika, “is where the controls for movin' these walls are?”
But since the walls had been lowered, that meant Mitsumura had already found them. She nodded and said “Right over here,” then led us back out of the maze, towards the exit. We followed behind her.
According to Mitsumura, the controls for the metal walls were in the archive. In one corner of the floor of the archive – a completely inconspicuous location – was a small lid recessed in the ground, behind which was a keyhole. Mitsumura told us the key to the archive fit the keyhole, and then proved it by taking the key from her pocket, inserting it, and turning it to the right. One of the bookshelves slowly slid off to the side, and behind it was a control panel, embedded in the wall.
Seeing that, I remembered how Mitsumura had taken so long to meet us and begin the summation of this locked room mystery, even though she'd been the one to call us there. I'd wondered at the time what she was doing, but she must have had a hard time finding this control panel. There was no way she could have demonstrated the trick without it. That was why she'd taken so long. Or would it have been more appropriate to say “she found it so quickly”? I wouldn't have been able to find such a well-hidden panel if I'd had a week.
As I stood thinking all that, I looked back at the panel. It had an LCD display and eleven buttons, a keypad showing 0-9 and an Enter key. When Mitsumura hit Enter, a four digit number appeared on the screen. When she hit Enter again, the number disappeared, and a different one flashed to replace it.
“It seems a different number is displayed every time the Enter button is pressed,” said Mitsumura. “It appears to be completely random. Incidentally, if you don't do anything, the number will disappear after ten seconds.”
Just as she said that, the number on the screen disappeared. Mitsumura hit Enter again, and another number appeared on the display. This time it was 9926.
“If the operation isn't completed within ten seconds, the number will be reset, so you have to enter it quickly. The method itself is simple enough to be intuited without needing to be explained. Just enter the same numbers as the ones displayed, then press Enter within ten seconds.”
As Mitsumura explained, she used the keypad to enter 9926, the same number being displayed on the screen, then pressed Enter. The numbers on the display disappeared, to be replaced with the word “COMPLETE”.
“And that completes the operation,” Mitsumura said casually. “The moment that is done, the metal walls of the underground maze begin to move. Once the input is complete, the walls descend – or ascend. And as we've already confirmed, the door to the room with the descending ceiling locks, as well.”
I remembered when Mitsumura and I had almost been crushed beneath that ceiling. So that was how the door was locked, preventing our escape.
Looking back at the display on the control panel, it was now showing the word “LOCK”. So while the walls were in motion, the panel was locked, making it impossible to stop the descending ceiling halfway.
“This concludes my explanation of the Locked Underground Maze. Are there any questions?”
With that, Mitsumura turned the key still in the keyhole to the left. The bookshelf slid back into place, covering the control panel on the wall.
After seeing all that, we exchanged looks before wordlessly nodding. We understood the trick perfectly. The Locked Underground Maze had been solved. The only question left in the case was who the culprit behind all these locked room murders was.
“I already know that,” said Mitsumura. “We have all the data we need to identify the culprit. So, allow me to solve the final mystery in Yatsuwako Village.”