At the scheduled hour, Yan, Qinghe, and Gu descended beneath the old celestial approach. Wei stayed above with the guard team and sealed the entrance against unauthorized entry. A narrow chalk line marked the path that remained clear for retreat.
“If the brace moves, come up at once,” Wei said. “We will not hold the shaft open.”
Yan nodded. He carried the pressure gauge; Qinghe had her instrument case, and Gu carried the original theory inside a waterproof sleeve. Two entrance guards remained at the top of the stairs. They would send a signal if another crack appeared.
The lower steps had been walled off for centuries. The stone was cold and smelled faintly of old metal and ink. Gu stopped at the first landing and compared the carved symbols with those in the island archive.
“This mark is older than the Registry furnace,” he said. “It points behind the steps.”
Qinghe checked the air and examined the support ribs before anyone moved farther. She found no fresh dust near the joints, but one rib had a hairline split. She tied a small white thread to it so they could see if the crack widened.
Yan tapped the wall with the side of his hand. One section gave a hollow sound. He knelt and tested the mortar. It crumbled under his thumb.
