Entry hall 411 was an austere, elongated gallery whose walls were ribbed with upright copper channels that carried air from the high outer chimney pipes down into the lower drainage chambers.
The air here was freezing, scented with the acrid bite of scorched oil and the dry, powdery stench of crushed dark rock. Every surface was coated in a fine, talc-like layer of black stone dust that had drifted down from the ceiling vents, settling over the flat stone slabs like dark snow.
Qiao Ming moved along the western wall, his bare feet leaving clear, pale footprints in the black dust. In his right hand he carried the twelve-pound lead weight, its braided horsehair cord looped three times around his forearm. His left hand rested upon the casing of his Folded brass star-compass, feeling the nonstop, high-pitched flutter of the internal sound chest muscle.
Behind him, Yan Zhiqiu stepped with silent, calculated grace, her boots stepping exactly into his footprints to keep their trail narrow and contained. Her horn recurve bow was held across her breast, an iron needle-point arrow resting lightly against the arrow-pass, her thumb hooked into the silk-bound ring on her string hand.
High above them, within the upright throat of Copper Flue Nine, the scraping sound intensified.
