A deep hum rolled through the wall beyond the control chamber. Dust fell from the ceiling in a fine curtain. The pale lines on the floor began moving toward the sound.
Luo called the group back. Gu held up a hand and listened.
He set his sketch against the wall and tracked the sound as it moved. The pulse crossed behind the visible corridor, paused, then returned along a different seam. Dust sifted from the ceiling at each return.
“Is that the same timing as the gate?” Yan asked.
“Close, but not identical,” Gu said. “The gate was one pulse. This is several.”
Luo moved the candidates away from the wall. “No one stands under the loose stone. Wei, count the pairs again.”
Wei called each name. The responses came from the junction and the exit. No one had moved deeper into the hall.
The next pulse made the floor lines slide toward the sound. One candidate started to step after them, then stopped when Wei raised his hand.
