The Lilliput Protocol

Beneath the granite avenues and copper spires of an industrial metropolis, a hidden subterranean facility hums behind miles of ammonia coolant lines. The state claims its high-precision naval torpedoes and automated telegraph networks are triumphs of mechanical theory. In reality, the entire grid relies on hundreds of thousands of hyper-dense artisans forced into perpetual hypothermia to keep their joints rigid and compliant.
When an uncredited municipal blueprint from forty years ago surfaces in an archivist's desk, a municipal scholar and a determined record-keeper cross paths with a fugitive fitter who survived the lower drainage lines. Marked for immediate disposal by internal security squads with pneumatic carbines, the unlikely pair is driven deep beneath the bedrock mantle into the freezing dark of the lower tiers.
To survive the descent, they must bypass autonomous clockwork sentinels, cross boiling chemical sumps, and face the bureaucrat determined to preserve the cold balance at any human cost. With structural fractures echoing through the stone and thirty tons of pressurized fluid trapped in the mains, their only weapon is the mechanical truth behind forty years of unacknowledged labor.