But Song Ning was gone, and so were those people.
All that remained in the factory building were Li Zekun's body and a furnace of molten iron slowly cooling.
Gu Zheng circled the area around the building several more times but found no more marks left by Song Ning.
He went back inside to search again and finally found the mark beside the knife switch.
He pulled the switch down and saw the tunnel entrance.
Only then had he followed her down.
"You mean that when you reached the factory building, the iron plate in the corner was closed, and the molten iron had cooled?"
Song Ning specifically asked about this as she listened to Gu Zheng's account.
Gu Zheng nodded. "Yes! I didn't see the tunnel entrance at first. It wasn't until I saw the mark beside the knife switch and pulled the switch that the entrance appeared."
"Just as I thought, they have an interconnected control system here. Earlier, the tunnel entrance only appeared after I closed the switch. That means it wasn't necessarily because someone had touched it. Either the entrance has a timed mechanism that closes it automatically after a certain period, or there's another control somewhere else."
Song Ning continued, "And when I came down, not only was the tunnel entrance open, but the molten iron was still bubbling. Yet by the time you arrived, the entrance was closed and the iron had cooled. That proves the furnace also stops burning after a certain amount of time..."
Gu Zheng picked up where she left off. "The tunnel entrance and the furnace door are both electrically controlled. They probably have another control panel linked to this equipment. When they retreat, they only need to pull the main switch, and everything returns to its original state. That