The sound was unlike any ordinary clockwork latch. It began with a low, underground groan that shook through the limestone floorboards beneath their boots. It was followed by a sharp, wet hiss. SHHH-TOCK. High in the four corners of the barrel-vaulted ceiling. There, the stone arches joined the central spine of the roof, four heavy copper air-flow flappers slammed shut inside their granite housings, seated firmly against thick collars of boiled leather impregnated with animal fat and beeswax.
Tomas swung his dark-lantern upward, its focused amber beam cutting through the drifting cloud of mold dust. At each corner of Bay Fourteen, six feet below the crown of the vault, sat a circular opening eighteen inches in width, lined with a collar of heavy cold-drawn copper. Across the mouth of each channel rested a circular copper plate half an inch thick, held tight against the stone rim by an external iron balance weight arm.
The air current in the room died instantly.
A moment earlier, there had been a faint, barely noticeable drift of cellar air moving from the high chimney pipes down toward the drainage gutter. A sluggish breath flow that at least carried away the heat of their bodies and the smoke of their spirit-lamp. Now, the air became dead, flat, and motionless. The smell of sixty years of rotting thick parchment, sulfur-tanned binding leather, and coal soot seemed to concentrate with sickening speed, hanging in the damp chill like an invisible woolen shroud.
