I'm doing engineering in the instance.

The freight elevator shaft was narrower than he had imagined.

It's not the kind of narrow that makes it difficult to pass through, but rather a compact design—in old industrial facilities, the dimensions of freight elevator shafts were based on the size of the goods, not on human comfort. The distance between the inner wall of the shaft and the metal ladder was about 60 to 70 centimeters. You could pass sideways without any problem, but you couldn't turn around. You could only go up or down one person at a time, not side by side.

Xie Chengzhou goes first.

The metal of the ladder was cold; so cold that his palms felt a tingling sensation for a second when he gripped it, before he adjusted. He held the flashlight under his armpits, alternating between gripping it with both hands, landing on his toes first on each rung, shifting his weight only after he was firmly on the ground. The distance from the third floor to the first floor was about twelve meters, with approximately thirty-six rungs. He had calculated this before starting his descent; at his current speed, it would take about fifty seconds. Including the start and stop, the entire descent would be completed in under one minute and twenty seconds.

However, while climbing the ladder, he did not check the contact between the hammer and the ground.

This was the first time he had lost the sensation of vibration since leaving the third-floor corridor.

He didn't panic; instead, he shifted his attention to another path—he gripped the rung of the ladder with his right hand, while lightly pressing the inside of his right wrist against the vertical main beam. The metal main beam was continuous from top to bottom, and the vibrations transmitted along it were more efficient than those from concrete, but the frequency characteristics were also different. He had noticed this phenomenon in Chapter 5: iron transmits high-frequency complex signals, and the two-second interval rhythm is still there, but it's different from what's transmitted through concrete, requiring a re-establishment of the judgment benchmark.

He took about seven seconds to complete this benchmark calibration during the descent.

The factory supervisor is on the southeast side, and the rhythm is two seconds per step, without any change.

He continued to descend.

The moment he landed on the first floor, his feet touched down first, and he slowly shifted his weight to prevent the impact from spreading through the floor. He let go of the crossbar, steadied himself, took the flashlight from under his arm, and shone it upwards—the other player was still climbing the ladder, about four steps away from the first floor. His descent posture was correct, alternating hands and keeping his center of gravity low, but his right foot landed slightly harder on the crossbar each time than his left. This was a matter of habit, not technique, and he probably wasn't aware of it.

Xie Chengzhou dimmed the flashlight by half and waited.

Level 4, Level 3, Level 2, Level 1—

The other person landed, right foot first. This time, the force was better controlled than on the ladder, and the sound was very soft. But as he released the ladder rung, the back of his hand brushed against a protruding bolt head on the inner wall of the shaft. The metal collided with a low-frequency, short, but clear "thud." At the same time, there was a burning sensation as it brushed against the outside of his hand. It wasn't deep, but the skin was scraped open, and he could feel the heat—he didn't look down, suppressing the feeling and focusing on the sound first.

Xie Chengzhou immediately pressed the cone-shaped head of the testing hammer into the ground.

Signal: Factory monitoring, southeast by east, rhythm normal, speed unchanged.

He waited three seconds. Four seconds. Five seconds.

The rhythm remained unchanged. The factory supervisors did not enter a state of alert.

Xie Chengzhou breathed a sigh of relief, but it was an internal one; his expression and posture remained unchanged—he simply removed the detection hammer from the ground and gestured for the man to walk south.

"Be gentle," he whispered. "Don't use the back of your hand on the bolts later."

The person nodded without saying anything.

The air on the east section of the first floor was more humid than on the third floor, carrying a familiar smell—rust, stagnant water, corroded rubber, and that specific, unmistakable mixed smell of a construction site that had been shut down for six months. He had already walked through this section when he first entered this unknown space, and what he had noted in his memo was: "East section: structurally intact, main passageway accessible, edge of the chemical area on the right side of the corridor, about eighteen meters from the end of the east section, acoustic amplification zone."

Now they are heading south, bypassing the core area of ​​the chemical zone, but passing its edge.

He mentally reviewed the route: the landing point of the freight elevator shaft → about 2.3 meters south → turn right into the main passage → walk south along the main passage for about 31 meters → reach the entrance to the south power distribution room. The entire route was about 54 meters long, including a section of about 8 meters that required passing the edge of the chemical storage area—the acoustic amplification factor of that area was 2.1 to 2.3 times, which fell within the coverage area of ​​implicit rule C. He had verified in Chapter 3 that in that area, a normal footstep would be amplified to a level similar to "stomping feet in a quiet corridor."

You don't have to take a complete detour, but you should go slowly.

He began to walk, maintaining low-frequency contact between the hammer's conical head and the ground, touching the ground every three steps to maintain continuous awareness of the plant supervisor's location. The plant supervisor was located southeast of his current position, approximately 41 meters away. The patrol route was between the southern and eastern sections, and he was currently on the section turning east. This meant that the plant supervisor would not approach the direction of the southern power distribution room for the next six minutes or so.

He noted in his memo: "T=0, factory monitoring southeast of south, about 41m, facing east. About 6 minutes from the power distribution room window."

The person was two meters behind him, their footsteps precise and steady. On the third floor, the other person learned to place their feet where Xie Chengzhou had stepped—not a complete copy, but a variation based on understanding the logic: their feet landed near areas "confirmed to be safe," rather than at random points. This was someone who learned quickly, and Xie Chengzhou labeled this person "Companion L" in his memo.

They walked to the edge of the chemical area.

Xie Chengzhou slowed his pace to one-third of his normal speed, landing precisely on the bare concrete surface he had already confirmed in Chapter One—no gravel, no sludge, no residue from chemical containers. He lowered his breathing rate, minimizing the rise and fall of his chest.

After walking for about thirty seconds, we passed the edge area, which is eight meters wide.

Then, behind him, he heard the faint sound of gravel rolling.

It wasn't loud, but at the edge of the chemical area, the sound was amplified into a clear, resonant "crack" that lasted for about 0.8 seconds.

Xie Chengzhou immediately pressed the testing hammer to the ground.

The factory supervisor, southeast by south, had a normal, unchanged rhythm. One second, two seconds, three seconds—he was waiting for that "prolonged rhythm during alertness." Two seconds, two seconds, two seconds.

The monitoring system remained unchanged. The sound of the gravel did not fall within the core area of ​​the acoustic amplification, but only at the edge, with the amplification factor between 1.2 and 1.4 times, which did not reach the threshold to trigger the monitoring system's tracking state.

Xie Chengzhou waited for about six seconds to confirm that things were stable, and then continued walking.

"Stones," he whispered, "next time, test them with your toes first, lightly touch them, don't put your full weight on them."

The man didn't speak, but his pace changed slightly, becoming slower and more cautious.

The power distribution room was located at the end of the south corridor. It had double iron doors, larger than the control room doors, but in better condition—the hinges still showed signs of lubrication, and the rust was superficial, not chemically bonded. The gap between the two doors was about three millimeters. He inserted the flat end of the testing hammer into the gap and gently pushed it open. The door on the left opened with a very quiet sound, less than expected.

He went inside.

The light in the power distribution room was almost zero.

Xie Chengzhou swept the area with his flashlight, allowing his gaze to make an overall assessment before focusing on the details—a habit he had developed on construction sites. When entering a new space, he would first spend ten seconds doing a global scan before focusing on specific locations to prevent overlooking potential risks in the overall structure due to premature focusing.

While performing a global scan, he glanced down at the back of his hand.

There was a red mark about two centimeters long where the bolt had scratched the skin; the skin was scraped open, and a little blood had seeped out, dark in color and already starting to clot. It wasn't deep, and the skin wasn't broken, but the heat lingered, as if the skin was reminding him that this wasn't over. He gently pressed the back of his hand against his trouser leg, absorbing the surface blood with a cloth, and then continued scanning the electrical room. That was it for now; no disinfection, no bandaging materials, this was all he could do for now.

The power distribution room was about five meters by eight meters, smaller than he had expected, but the layout was reasonable: the main power distribution cabinet was on the west side, a large floor-standing unit with an iron casing, about two meters high and three meters wide, with several circuit breakers on the cabinet panel, most of which had tripped, with only the rightmost row remaining closed; against the wall on the east side were several rows of abandoned control panels, covered in dust; on the south side was the outgoing cable well, with the cables neatly bundled, the outer sheaths aged but not obviously damaged; on the north side, the direction he came from, were double doors.

Where is the main switch?

His gaze fell on the top of the main power distribution cabinet.

It's not a circuit breaker, nor a control panel; it's a large knife switch installed on the top left side of the distribution cabinet, secured by a metal bracket. The blades are mounted vertically, and the handle is a cast iron operating rod about 30 centimeters long. The current state is "disconnected"—the blades are facing upwards and detached from the stationary contacts below. The contact surface has a noticeable oxide layer; it's gray and glossy, a characteristic color of oxidized copper.

He pointed the flashlight at the lever switch, looked at it for about twenty seconds, and made several assessments.

First, the contact oxide layer. The contact resistance of copper oxide is about one to two orders of magnitude higher than that of copper. At the moment of activation, the arc will be stronger than normal, and the sound and light produced will exceed normal levels—he needs to estimate the magnitude of this sound. According to the nameplate of the distribution cabinet (the handwriting is blurry, but the "200A" is still legible), this is a 200-amp main circuit switch. The arc sound produced when activated is about 85 to 95 decibels in a quiet environment. Considering the additional impedance of the contact oxide layer, the estimated actual value is closer to 100 decibels, lasting for less than one second, followed by the noise of the equipment starting up after the main circuit is connected.

Second, operating force. The cast iron operating lever of the pull-tab switch involves pressing down – pushing the blade from the "off" state into the stationary contact to close it. Ergonomically speaking, for a 200-ampere pull-tab switch, the operating force is approximately 20 to 30 Newtons. Considering the increased friction due to the oxide layer on the contacts, this is estimated to be 30 to 40 Newtons, with a continuous force application time of approximately 0.8 to 1.2 seconds.

Third, the trigger signal. According to the notes in Gu Zeyan's report, after activation, the plant supervisor's thermal sensor will immediately respond and retract its patrol range to within about 22 meters. He is currently standing about 1.5 meters from the main switch, and the entrance to the power distribution room is about 4 meters from his current position. He needs to move to a distance of more than 22 meters from the main switch after activation and before the plant supervisor's thermal sensor retracts to its full position.

He did a quick mental calculation: from the power distribution room, it would be about fifteen meters north along the main passage, plus the time to activate the moving window. He had indirectly estimated the response time of the plant supervisor's retraction in Chapter Three—the response of the thermal sensing system wasn't instantaneous; after the other person who triggered the event stepped on the chemical area, the plant supervisor paused for about one and a half seconds before switching to the tracking route. That one and a half seconds was his most precious time buffer.

Once activated, it will move to a distance of 22 meters within 1.5 seconds.

He had already planned the route. While waiting for those eight minutes, he mentally retraced the route from the power distribution room to the safety line eleven times. Where to land at each step, which step to turn, which step to stop—it wasn't anxiety, but a pre-construction technical briefing, something he did every time before starting work on a construction site.

他在备忘录里写：「配电室确认：主拉刀开关·200A·当前断开状态·触点氧化。激活声：估算约100dB，持续≤1s。操作力：30-40N，压入约0.8-1.2s。激活后移动：1.5s窗口，22m安全线，北行路线已确认。等待条件：厂监路线变更（下一次约8分钟后）。」

Then he glanced at L, the person who had followed him in. L was standing about two meters to his right, also looking at the main distribution cabinet. His expression was the same one he had seen before—not fear, but a brief moment of bewilderment, overwhelmed by the amount of information.

"How many times have you been to this instance?" the person asked, his voice perfectly controlled, almost a whisper.

"A copy? This is my first time," Xie Chengzhou said.

The other person was silent for a second. "This is the third time," he said. "The first two times I didn't go out, so I didn't know there was a main switch here."

Xie Chengzhou didn't ask, "How did you die?" The question was pointless; the result was the same—he didn't leave, twice. He simply said, "At the initial entry point, the factory's power supply lines were exposed on the south side of the ground. The main distribution cable was over 200 amps in diameter, indicating there must have been a separate distribution room located on the south side."

"I didn't notice the power lines."

"People on the construction site will pay attention," Xie Chengzhou said, "because stepping on exposed wires is a frequent cause of safety accidents on construction sites, so you are used to looking at the ground under your feet."

The person nodded, slowly processing the words rather than simply indicating that they had heard them.

Xie Chengzhou turned his attention back to the detection hammer. The factory supervisor, currently located approximately 38 meters southeast, was still on normal patrol, with no change in rhythm. The last route change occurred about 24 minutes before they entered the control room. Based on his calculated average change cycle of 32 minutes, the next route change was expected in about eight minutes.

He waited in the power distribution room.

During the wait, the player remained silent, only occasionally glancing from the main power distribution cabinet to the doorway and back again. Xie Chengzhou noticed that his hands were on his knees, his fingers unconsciously clenching and unclenching, a gesture he had seen many times on construction sites—not fear, but the kind of state where one "knows what is going to happen, but still can't control their body's preparation for stress."

Xie Chengzhou didn't say anything, because there was nothing to say. Waiting is just waiting; it doesn't need explanation.

Approximately seven minutes and twenty seconds later, the route change signal arrived about forty seconds earlier than he had expected.

He didn't have time to analyze the reason, but he felt the change in rhythm: the "pre-compression" signal from the detection hammer was abnormal - instead of once every two seconds, the interval between two consecutive "pre-compression" signals was lengthened to 3.2 seconds, followed by a short pause that lasted for about two seconds. After that, the rhythm was re-established, but the direction was different. The direction of the epicenter changed from southeast to east to due west to south.

The route has been changed. The plant supervisor is moving southwest, away from the power distribution room.

Xie Chengzhou stood up.

The player also stood up; he was ready and it was clear he was waiting for this signal.

Xie Chengzhou walked towards the main distribution cabinet, held the flashlight between his left arm and chest, aimed the beam at the pull-out switch, first held the test hammer upside down with the cone head facing up in his right hand, placed it on the table on the right side of the distribution cabinet, and then held the cast iron operating lever with both hands.

Just as his hand touched the joystick, the other player reached out.

It wasn't to help, it was to stop him. Her hand rested on his right arm, lightly, but with a clear intention. "No," he said in a very low voice, "it's too loud, the factory supervisors will come."

Xie Chengzhou didn't look at him.

He knew what this person was thinking—in his previous two experiences, loud noise equaled death. This was a rule he had learned with two lives; it was ingrained in his body, not a rational concept, but a reflex.

"Let go," Xie Chengzhou said, enunciating each word clearly. "I've calculated it."

The other person's hand paused for a second, then released it.

Xie Chengzhou began to apply force, pressing down slowly and steadily.

The control lever was cold, colder than a ladder, a deep coldness unique to cast iron, not the coldness of the metal surface, but the coldness brought about by the density—he had dismantled similar old equipment at construction sites before and knew this feeling. He had to grip it a little tighter in his palm to prevent it from slipping when his hands were sweaty.

For the first three seconds, nothing happened; the lever didn't move. But he could feel the elastic resistance coming from the lever—it wasn't completely rigid. Cast iron has a slight elastic deformation, and when the force approaches its limit, the lever will bend a little bit before breaking through.

In the fourth second, the control lever moved slightly, by about five degrees.

In the fifth second, the blade began to move downwards, contacting the oxide layer on the surface of the stationary contact point, producing a very slight frictional sensation that traveled into his palm.

Then comes the electric arc.

It was louder than he had estimated—not ninety decibels, but closer to one hundred decibels, a short, metallic bang, like the sound of a metal rod being instantly welded to another metal, lasting for about 0.7 seconds, and then stopping.

The main circuit is connected.

A slight humming sound began to emanate from the outgoing cable on the left side of the power distribution room. This was caused by electromagnetic induction after the high-voltage line was energized, with a frequency of about 50 Hz. Xie Chengzhou identified it in his ear and marked it as "normal". Then came the sound of equipment starting up from deep inside the factory on the first floor—the sound of relays clicking, "click", "click-click", three or four of them, distributed in different directions of the factory.

At the end of the south corridor, an emergency light came on. It was orange and dim, but in the complete darkness, the orange light brought the outline of the entire corridor back into focus.

Xie Chengzhou is already moving.

He released the lever the instant it was fully depressed, and without waiting for confirmation, walked straight to the door. His timing was based on the sound of the electric arc—he had 1.5 seconds from the moment the arc ended.

"Stay close," he said.

He didn't run, but his pace was the fastest he had ever walked in this instance, and his footsteps were still precise, each step landing precisely on the spot he had already rehearsed in his mind.

Leave the power distribution room, take the main passage, and head north.

He heard about the changes in the factory supervisor during the seventh step.

The rhythm is out of control. It's not a gradual change, it's a sudden change—from a two-second interval to an irregular, rapid vibration rhythm with rapidly changing directions. The "pre-compression" signal in the detection hammer has become a dense, overlapping pattern, losing the distinctiveness of a single step. This is a tracking state, but it's not coming towards him; the plant supervisor is directionally locating the arc sound—it's rotating, searching for the heat source.

Xie Chengzhou counted the steps: eight steps, nine steps, ten steps—

His steps are 1.1 meters, ten steps are eleven meters, and he is still eleven meters short.

Behind him, he could hear the footsteps of his companion. Xie Chengzhou didn't turn around, but judging from the sound of the footsteps, the other person was about two steps behind him, roughly a two-meter difference.

Thirteen steps, fourteen steps, fifteen steps—

The monitoring rhythm of the plant has stabilized, turning into a rapid, directional approach signal—it has found its direction, heading south, toward the power distribution room.

It wasn't coming towards him. The heat source of the electric arc was in the electrical distribution room, not him.

Xie Chengzhou slowed down and stopped at the eighteenth step, touching the test hammer to the ground to confirm his position. His current position was about twenty meters from the main switch, two meters outside the safety line—plenty of room.

The plant supervisor is moving towards the power distribution room at a speed significantly faster than during a normal patrol. The amplitude of his footsteps is about three times that of a normal patrol, which is a characteristic of tracking – a lower center of gravity, a larger stride, and a faster speed.

He turned around.

The player stopped at the sixteenth step.

Xie Chengzhou glanced at his position: about 22 meters from the main switch, right on the edge of the safety line—but "edge" is not "outside". If the plant supervisor's current tracking route is directly into the power distribution room, it will pass through that direction, and the thermal scanning radius is 22 meters. The person standing there is right on the scanning boundary.

The factory supervisor's footsteps grew closer and closer, reaching the intersection of the main passage and the southern corridor, about twelve meters from the power distribution room and about eight meters from his companion.

Xie Chengzhou took two steps back.

He didn't think too much. He reached out, grabbed the back of the man's shirt collar, and pulled him back forcefully, about 1.5 meters. The man staggered and almost lost his balance, but managed to keep his footing and didn't fall or make a sound. He simply stood next to Xie Chengzhou, about half a step away.

Two people stood in the main passage, 23 meters away from the main switch. The factory supervisor entered the power distribution room about 6 meters to their south.

Stopped.

Xie Chengzhou could sense the stillness from the signal from the detection hammer—the footsteps stopped, and there was a slight vibration in place. It was the factory supervisor scanning at the entrance, with the thermal sensor covering the radius. There were no biological heat sources in the power distribution room, only the heat generated by the equipment that had just been powered on.

The temperature characteristics of heat dissipation are different from those of biological heat sources.

Five seconds. Ten seconds. Fifteen seconds.

The factory supervisor paused at the gate for about twenty seconds, then the rhythm re-established, slowly—he could feel this change in rhythm from tracking back to normal patrol in the vibrations, the process of the intervals widening from irregular to two seconds per step, was a deceleration, not a break.

It gave up.

Xie Chengzhou removed the testing hammer from the ground.

The factory supervisor turned around at the entrance of the power distribution room and began to walk its patrol route again. The amplitude of its footsteps dropped from the large strides of the tracking state back to the rhythm of normal patrol, one step every two seconds, heading east and north, entering the route it had walked countless times in this factory, as if nothing had happened.

Then the lights in the factory came on.

Not just one lamp, but all of them.

Those fluorescent tubes had been used for who knows how many years, and most of them were old and discarded. But the moment the main circuit of the entire factory was connected, those that were still working lit up. It was the unstable flickering produced by the old fluorescent tubes the moment they were powered on, green and white, illuminating every corner of the factory with a color that was both real and distorted.

Xie Chengzhou stood there, looking at the lights.

Then he saw the factory supervisor.

It's not through a testing hammer, not through vibration signals, but directly, visible to the naked eye.

Before the lights came on, all his knowledge of the factory surveillance came from the vibration signals under his feet—rhythm, location, speed, direction, characteristics of the tracking status, and patterns in the patrol routes. He treated the factory surveillance as an engineering parameter, a variable that could be modeled, avoided, and utilized. He never thought of looking at it.

Now he sees it.

At the other end of the corridor, bathed in the flickering fluorescent lights, stood a man in an old-fashioned factory safety uniform, white, the kind of white that has faded to a yellowish hue over time. He wore a hard hat, the brim slightly low, casting shadow over the upper half of his face. Below the brim, he could see a person's facial structure—where the eyes, nose, and mouth should be, everything was correct in shape, size, and proportion.

But there was nothing inside.

It's not blurry, not damaged, not because it's too far away to see clearly—it's a more fundamental lack than simply not being able to see clearly, like a sketch of a face where all the lines are drawn correctly, but nothing is filled in.

Xie Chengzhou stood there and stared for about three seconds.

The factory supervisor didn't look at him. Or rather, it didn't perform the action of "looking"—it was blind, it didn't see, it only sensed, sensed heat, sensed sound, sensed vibration. That blank face faced straight ahead, calm, without any expression, because there were no organs to form expressions.

Then, taking one step every two seconds, it continued walking.

Following its patrol route, its stride was uniform and its rhythm steady, disappearing around the corner of the corridor. The lights were still flashing, and its helmet swayed slightly with its steps, until the last part of its silhouette was also obscured by the corner of the corridor and disappeared.

It was as if it had never known that Xie Chengzhou and that player had walked through this factory.

Xie Chengzhou wrote in his memo: "Factory supervisor's appearance: Factory safety uniform, white (aged), safety helmet, low brim. Face: Complete structure, no details, correct lines, missing content. Speculation: This is a template for the factory worker's appearance. To be verified: The reason why the designer retained the worker's appearance."

Next to that line, he wrote in parentheses: "(First time seeing it clearly.)"

He no longer needed his flashlight, so he turned it off. In this space, the fluorescent lights were sufficient, even though their light was greenish-white, flickering, and carried an old-fashioned feel.

He turned his head and glanced at the player.

The other person was beside him, not speaking, also looking in the direction where the factory supervisor had disappeared, with an expression that he couldn't quite describe—not fear, but the kind of expression that said "something has been completely altered," a brief blank after a person's cognitive framework has been quietly replaced in a certain moment.

"It's over," Xie Chengzhou said. "It's over as planned."

The player took about three seconds to turn his gaze from the corner of the corridor and look at him. "You cleared the game on your first try."

This is not a question.

Xie Chengzhou did not answer. This observation was complete and needed no further explanation. He put away the memo, returned the testing hammer to his waist, and then mentally reviewed the structural assessment of the factory building one last time—from the initial assessment upon arrival to the current final state, identifying where it matched expectations, where there were deviations, and the sources of those deviations.

Occupational hazard. He knew it.

But the data is there, and it's a waste not to organize it.

He wrote a few technical notes in his memo, then took out the entry time, calculated the time difference once, calculated it a second time, and confirmed the numbers.

He wrote it down, circled it, and then wrote four words next to it: "Time taken to clear the checkpoint".

Eighteen minutes and forty-seven seconds.

Then at the very bottom of the page he wrote: "Site completed."

He wrote those four characters with a little more force than usual, not out of emotion, but out of habit—he wrote them like this on the last page of every completed project report, with a little more force, to make it seem solemn, to make it seem that the matter was actually completed and not just written on paper.

Inside the factory, the factory supervisor's footsteps echoed from afar in the corridor, still every two seconds, with the same rhythm, exactly the same as when he came in.

The ground vibration on the first floor has stopped. The extremely slight, continuous low-frequency vibration has stopped. Xie Chengzhou recorded it in the first chapter as "factory foundation vibration: source unknown, speculated to be the accumulation of floor resonance caused by long-term patrols by factory supervisors". Now it has stopped, stopped silently. He only realized it was gone in a moment. He no longer needed to treat it as background noise.

He stood in the brightly lit factory corridor, going over everything in his mind one last time, then put away the memo and walked towards the exit.