The final threads of the tallow candle wick sputtered out against the cold iron rim of Maya's drafting table, leaving only the fierce, amber glare of the primary manifold gauge to illuminate the final hours of the seventy-two-hour clock.
Inside Sub-Level 7, the ambient air had plateaued at ninety-eight degrees Fahrenheit, dense with the scent of hot linseed oil, wet granite, and the unmistakable metallic sharpness of high-pressure mineral steam.
Maya's hand was steady as she made the final ink entry in the sector logbook, her fingers stained with black graphite and red sealing wax.
"Twenty-eight minutes remaining on Sterling's ultimatum," she said quietly, her voice carrying clean across the vibrating deck plates to where Danial stood at the central console. She didn't look up from her ledger, but her brass compass clicked once as she closed its arms and slid it into her leather harness. "If the High Glass council follows standard Directorate doctrine, they won't send a herald down the lift shaft to ask for our surrender. They'll signal the battery the exact second the clock strikes six."
Danial did not answer immediately. He was bent over the open inspection hatch of the lower bypass valve, his right hand gripping an eleven-inch iron wrench as he made a quarter-turn adjustment to the packing nut on the secondary hydraulic ram.
The iron nut creaked under the torque, settling into place with a sharp CLICK that registered through the metal soles of his work boots.
"The packing nut is tight," Danial said, straightening up and wiping his brow with the back of his scorched leather glove. He looked toward the northern bulkhead, where the twelve-foot-thick barricade of salt-bags, oak timbers, and steel I-beams stood silent, blocking the primary access gate. "The four ceiling rams are holding thirty-four pounds of live pressure. If Commander Kren fires his five-inch mortars, the hydraulic cushion will take the first shock wave without dropping line head to Sector 4."
"He won't fire just one round, Vance," Old Man Oakes grunted from his seat near the base of the primary boiler shell. The old miner was wrapping tight strips of tarred canvas around the handle of his iron-tipped staff, his knuckles swollen from forty years in the salt vaults. "Kren was a battery master at the North Breach in '82. He doesn't fire for sighting. He loads four guns in sequence, walking the shells across the ceiling arch five seconds apart to create a resonance wave in the rock."
"Let him walk them," Gears bellowed from the catwalk above, his voice echoing through the riveted iron girders. He was standing beside the two high-pressure steam cannons mounted through the gun-ports of the barricade, his hands resting on the bronze quarter-turn valves. "The moment his shells hit the upper slate, I've got six hundred degrees of superheated head waiting to blow straight up that lift shaft! If his sappers try to follow the artillery down the stairs, they'll walk into a wall of live vapor that'll melt their iron breastplates!"
"Keep those steam valves locked until I give the command, Gears!" Danial called up, his voice cutting through the hollow roar of the manifold. "If we dump the secondary header early, we drop back-pressure at Node 6, and the thermal sink in the central spire will lose its siphon prime. We hold the pressure until the ceiling takes the first hit."
Three hundred yards above, on the Level 3 battery deck of the High Glass access shaft, the atmosphere was dead silent save for the rhythmic, mechanical ticking of Commander Kren's brass firing chronograph mounted to the rock wall.
The four five-inch iron siege mortars stood aligned in a dead-straight firing line, their thick barrels angled sharply upward at seventy-eight degrees, trained directly into the dark vertical mouth of the ventilation shaft leading down to Sub-Level 7.
Behind each gun stood three 3rd Iron-Clad Sappers, their leather ear-flaps buttoned tight, their heavy lead-lined aprons buckled across their chests. Each loader held a fifty-pound cast-iron delayed-fuse shell cradled in his arms, the brass nose-cone timers pre-set to three-point-two seconds—the exact time needed for a gravity-assisted fall to reach the upper ceiling arch of Node 6.
Captain Vane stood on the upper gantry platform behind the battery, his pocket watch open in his left palm, his right hand holding a raised silk signal flag. Beside him, Commander Kren held a glowing friction igniter cord, his scarred face illuminated by the pale white glare of two magnesium torches mounted to the bedrock anchors.
"Ten seconds," Vane announced, his voice devoid of emotion, his eyes fixed on the sweeping sweep-hand of his silver watch.
Across the platform, the sappers stepped up to the mortar muzzles, their boots set wide on the iron plates, waiting for the command.
"Five seconds," Vane said. "Four... three... two... one."
Vane dropped the silk flag with a sharp downward snap.
"BATTERY... FIRE!" Kren roared, slamming his ignition torch down onto the primer touch-hole of the lead mortar.
BOOM!
A deafening, orange blast of flame and black powder smoke erupted from the first mortar barrel, illuminating the entire vertical shaft in a blinding flash. The thousand-pound cast-iron carriage slammed back against its granite foundation pins with a violent CRACK, the heavy iron recoil springs screaming under the sudden kinetic load.
Before the smoke from the first gun could clear the gantry, Kren touched the igniter to the second, third, and fourth muzzles in rapid, five-second intervals.
BOOM! BOOM! BOOM!
Four fifty-pound armored shells plunged down the narrow dark throat of the vertical ventilation shaft, their brass delayed-fuses whistling a high-pitched, screaming song of death as they fell three hundred yards through the hot, pressurized darkness toward the subterranean fortress below.
Inside Sub-Level 7, the warning didn't come from sound; it came from the sudden, sharp drop in atmospheric pressure that pulled the air straight out of Danial's lungs a fraction of a second before impact.
"COVER!" Danial screamed, lunging across the console desk and pulling Maya down behind the heavy green-enameled steel casing.
THUD-CRACK!
The first fifty-pound shell struck the upper slate seam sixty feet directly above Node 6's primary boiler.
The kinetic impact was catastrophic. A shock wave of solid energy traveled down through the basalt rock, radiating out in a visible wave of white dust and shattered stone fragments. But instead of the slate collapsing inward and dropping ten tons of overhead crane rail onto the steam headers, the newly installed four-inch hydraulic rams engaged instantly.
HISSS-BANG!
The thirty-two pounds of live thermal steam inside the four hydraulic cylinders compressed under the violent downward shock, acting as a massive pneumatic spring. The internal bronze pistons yielded four inches, absorbing the immense kinetic force of the shell, before the continuous pressure from the deep core forced the rams back upward, driving the slate seam back into place with a thunderous metallic recoil.
The second and third shells struck three seconds later, slamming into the rock arch in rapid succession: BOOM-CRACK! BOOM-CRACK!
Clouds of white salt dust and razor-sharp slate splinters rained down onto the iron deck plates, rattling off the boiler shell like canister shot. The heavy iron lamps suspended from the crane rail swung wildly in seventy-degree arcs, their yellow flames flickering wildly as the air inside the cavern vibrated with deafening, metallic thunder.
"THE SHORES ARE HOLDING!" Maya shouted from beneath the console, her hands covering her head as dust settled over her leather drafting board. She wiped her eyes, looking up at the brass pressure gauges mounted on the wall. "The steam rams absorbed ninety percent of the kinetic impact! The slate seam didn't breach!"
"FOURTH SHELL!" Oakes yelled from behind his salt-bag barricade, pointing his staff up at the shadowed vault.
The fourth shell—its delayed fuse detonating precisely upon impact—exploded directly against the upper granite anchor block with a blinding orange flash and a deep, gut-churning roar: KABOOM!
A five-ton slab of loose ceiling basalt sheared off the outer edge of the arch, plummeting sixty feet straight down toward the northern staging deck.
"WATCH OUT BELOW!" Gears screamed from the catwalk.
The massive rock slab slammed squarely onto the twelve-foot-thick composite barricade behind the northern bulkhead door. The oak shoring timbers groaned under the massive weight, the structural steel I-beams flexing two inches downward, but the eight hundred cubic feet of packed salt-slag bags absorbed the crushing force without bursting a single seam.
The heavy three-inch forged steel door remained sealed, its hinge pins intact, its deadbolts locked solid into the granite frame.
As the thundering echoes of the fourth detonation died away into the cavern walls, a heavy, thick silence settled over Sub-Level 7, broken only by the steady, rhythmic thud-thud-thud of the central core engine down the southern incline and the high-pitched whistle of escaping steam from the relief ports.
Danial Vance rose from behind the iron console, his clothes white with pulverized salt dust, his hands steady as he reached for his heavy iron wrench. He looked up through the swirling clouds of grey smoke to the high roof arch.
The four hydraulic rams were still there, glowing pale white-gold under the core's light, their bronze pistons fully extended, holding fifty thousand tons of mountain rock firmly on their iron shoulders.
"Maya," Danial said, his voice flat, hard, and cold as forged steel. "Check the line pressure to Node 6."
Maya wiped the white dust off the main dial, her fingers tracing the glass bezel. A fierce, unyielding smile broke through the soot on her face.
"Line pressure thirty-two pounds continuous," Maya reported, her voice ringing clear through the smoke. "Not a single PSI lost. Sector 4 still has its heat."
Danial turned his gaze toward the barricaded northern door, where the faint, frantic pounding of Captain Vane's retreating vanguard could be heard echoing faintly down the upper lift shaft.
"Gears," Danial ordered, stepping up to the catwalk ladder. "Open the secondary bypass ports by ten percent. Let Envoy Sterling know that his first salvo didn't even scratch the paint."