The sound of the drill was a high, shaking scream that set the teeth on edge.
Through the six feet of dark rock flanking the Great Iron Arch, the sound shaking reached Qiao Ming’s ears as a tiny, persistent insect whine—a metal skreeeeee that rose and fell in rhythmic three-second pulses. It was the characteristic sound of a high-speed heavy dark metal diamond drill. It was driven by a tightly packed-air-powered motor, boring into the cast-bronze bolts and pins of Drainage Chimney pipe 14.
Qiao Ming knelt on the dry flat stone slabs behind the arch, his left ear pressed against the cold face of the rock. His bare hands rested flat on the stone, feeling the tiny blast waves that traveled through the crystal-clear grain of the dark rock.
He unhooked his Folded brass star-compass, extended the aimed sound horn, and aimed it through the check slit.
The instrument confirmed his physical diagnosis: the drill was running at six hundred turns a minute, turning a two-inch heavy dark metal diamond coring bit against the intake grate of Chimney pipe 14. Five living signed names were gathered in the nook fifty paces beyond the iron gate—Zhu Heling and four heavily armored students or hired blades.
