At dawn, Gu knelt in the machine room with a brass rod pressed to the floor. The furnace’s uneven hum traveled through the metal into his palm. The channel map on the wall showed a branch running toward the outer barrier, but the sound turned south beneath the station.
Han brought the newest survey sheet. Everything south of the wall was marked as empty reserve land.
“We haven’t updated this since the settlement grew,” she said. “The boundary is old.”
Yan followed the pipe’s direction with his eyes. “Where does it end?”
Gu pointed south. “Somewhere we can’t see from here.”
Two maintenance cousins, Sui and Reng, lifted the access hatch under Han’s supervision. A narrow tunnel opened below the floor. Gu lowered a lamp. The copper line bent toward the town, and moisture beaded along the brick.
Qinghe handed the cousins clean jars. “Take a sample from the wall and another from the nearest well. Don’t touch the inside of the jars.” She wrote the time and place on each label. “We’ll compare them. I can’t tell what it is just by looking.”
Yan crouched into the tunnel to hold the lamp while Reng scraped water from the seam. A bead rolled down the brick. Yan reached to feel whether the wall was warm. Heat burned through his glove and bit into his fingers.
