The upper exit of the heat chimney pipe was not a doorway. It was a slaughterhouse disguised as an air valve.
At the four-hundred-foot summit of the upright shaft. There, the hot gases were supposed to vent into the Middle Walkway’s botanical gardens, stood the Great Clockwork Filter Gate.
It was a circular barrier of forged brass and cold-rolled steel, fifteen feet in width. It was built into a massive granite arch. In the center of the barrier, powered by the nonstop exhaust draft and a massive gear-train linked to an overhead balance weight, spun four pairs of five-foot crescent-shaped steel scythe-blades.
They rotated in counter-opposed orbits at three hundred revolutions a minute, their polished edges whistling through the steam with a terrifying, rhythmic snick-snick.
Where the blades intersected, there was no gap larger than a man’s thumb. Anything that tried to pass through the opening—a rat, an eagle, or a desperate weaver—would be cut into ribboned mince in less than half a second.
Mounted on the stonework wall beside the gate was an iron control stone stand, protected by a fine, detailed six-tumbler brass gear-lock.
“An anti-personnel scythe-gate,” Vane Vale noted. He leaned over the handrail and inspecting the whirling steel with clean, steady care. “Installed under the Vagrancy Suppression Act of Year Ninety-Two to prevent chimney-sweeps and under-city smugglers from entering the private boulevards of the aristocracy. Powered by a fifty-ton gravity balance weight. Without the town key-metal tube, the bypass can’t be tripped.”
