The milestone had been a point of obsession for the internal planners of Ashfall for months. One thousand souls. In the archaic ledgers of the Empire, a thousand citizens marked the transition from a mere outpost to a chartered town; in Kael's math, it was the critical mass required for a fully redundant industrial society. But as the brass counter in the command vault clicked over—the digits rolling with a soft, mechanical snick to show 1,000—the expected surge of triumph was instantly suffocated by a visceral, internal scream.
The warning didn't come from the Seismic Mirror or the Relay-Brain. It was the "Golden Finger," the primal intuition that had kept Kael alive since the first day of the frontier, now erupting into a deafening, white-hot roar at the base of his skull. It was a sensation of imminent, absolute annihilation.
"Seal the primary intake!" Kael's voice cracked the stillness of the vault, raw and jagged. "Now! Lock the secondary pressure-seal and kill the ventilation flow to Tier 1!"
Elms, his fingers stained with the purple ink of the population logs, froze. "But Baron, the tenth man—the thousandth soul—he's just stepped into the airlock. They're exhausted. If we kill the flow, the heat-spike alone will—"
"They aren't exhausted," Kael hissed, lunging across the console to strike the manual override.
Through the silver-mirrored periscope, the "grit" of the deception became visible in agonizing detail. The ten men standing in the transition tunnel were dressed in the same salt-stained rags as the hundreds who had come before them, but their posture was a lie. They didn't slump against the limestone walls with the heavy, bone-deep fatigue of the starving. They stood in a "Low-Ready" tension, their weights centered, their eyes scanning the iron rivets of the airlock with a professional, predatory focus.
Kael focused the lens on the lead man's boots. Most refugees arrived caked in the grey-white slurry of the marsh or the fine limestone dust of the lower paths. These men bore a thick, ochre-colored clay in the treads of their regulation-issue soles. It was the specific, iron-rich paleosol found only at the three-hundred-foot depth of the northern ridge.
"The sonic bore," Kael whispered, the cold logic of the warning finally crystallizing. "They didn't tunnel through the surface. They used the vibration-drill to create a 'Frequency Screen,' masking the sound of a high-speed micro-bore. They've come in under our seismic floor."
In the airlock, the lead infiltrator realized the inner door wasn't opening. The "starving" man reached into his tunic, and his movement was a blur of military precision. He didn't pull a blade. He withdrew a blackened iron cylinder, roughly the size of a flare, but intricately etched with silver galvanic traces.
The internal warning in Kael's head reached a crescendo of physical pain.
"It's a Pulse-Beacon," Kael gasped, his hand gripping the cold iron of the Vacuum-Purge lever. "He's not here to sabotage the door. He's going to transmit a high-frequency acoustic ping from inside our iron skeleton. If the sonic bore on the surface receives that ping, they'll have the exact harmonic coordinates of our primary support pillars. They won't have to shake the mountain anymore; they'll just 'shatter' the specific arches holding up the residential tiers."
The air in the command vault felt suddenly thick, smelling of hot brass and the ozone of the overtaxed Relay-Brain. Below them, in the communal halls of Tier 3, the muffled sound of cheering drifted up through the acoustic pipes—a population celebrating their thousandth member, unaware that he was currently holding the detonator for their tomb.
"Drax, get your men back from the inner seal," Kael signaled, his voice dropping to a low, lethal register. "We have a 'Black-Level' breach. Elms, initiate the Vacuum-Purge. Now."
"Baron," Elms's voice trembled. He was a man of mathematics and ink, not of blood. "If we evacuate the airlock while they're in it... the pressure differential will burst their capillaries instantly. There is no 'arrest' in a vacuum. It's an execution."
"They aren't here to be arrested," Kael said, his eyes fixed on the silver mirror.
The lead infiltrator was already kneeling, pressing the iron cylinder against the limestone floor. He was looking for the specific resonant contact point—the spot where the bedrock met the iron skeleton. If he triggered that pulse, the "Iron Skeleton" Kael had spent months building would become a conductor for its own destruction.
Kael didn't wait for Elms. He slammed the heavy lever downward.
The sound was a hollow, haunting thrum that vibrated through the floor of the command vault. It wasn't the roar of an explosion, but the terrifyingly quiet scream of high-pressure air being sucked into the mountain's secondary "Void-Sump." In the airlock, the transition was instantaneous.
Through the periscope, Kael watched the physics of a vacuum-purge take hold. The ten men didn't have time to scream. The air was ripped from their lungs with such force that their chests collapsed inward. The lead man, his hand still gripped around the Pulse-Beacon, clawed at his throat as the nitrogen in his blood began to boil, turning his skin a mottled, bruised purple. He slumped against the floor, the blackened cylinder rolling from his lifeless fingers.
The internal warning in Kael's head didn't vanish, but it shifted—the shriek of imminent death fading into a dull, thrumming ache. The immediate threat was neutralized, but the "grit" of the act hung in the air like a physical weight.
"The count," Elms whispered, his hands shaking as he looked at the brass register. "Does it... does it still stay at a thousand?"
"No," Kael said, his voice hollow as he watched the ten shadows in the airlock through the mirrored glass. "The count is nine hundred and ninety. We don't count ghosts as citizens."
The social impact was immediate and silent. Drax's intake guards stood on the other side of the inner seal, listening to the silence of the vacuum. They knew what had happened. They could feel the "void" through the iron door. For the first time, the citizens of Ashfall realized that the mountain wasn't just a shield; it was a weapon that Kael could turn on anyone, even those who looked like friends.
A technical failure manifested minutes later. The sudden, violent evacuation of the airlock had created a "Pressure-Kick" back through the ventilation system. The secondary bellows in the Bio-Foundry, unable to handle the sudden reverse-surge, had ruptured. A faint, sweet scent of medicinal alcohol began to drift through the tiers—a sign of the "Sanitary Shield" being compromised.
Kael didn't move. He kept his eyes on the periscope. On the surface, the Seismic Mirror showed the Imperial sonic bore's signature flickering and then going dark. Without the beacon's return signal, they were blind again. But Vane now knew exactly where the intake gate was. The "Shadow" tunneling had failed, which meant the next move would be a "Surface-Punch"—a massive, concentrated kinetic assault on the airlock's exterior.
"Clean the corridor," Kael commanded, his voice devoid of emotion. "Re-seal the vents. We need to reinforce the intake with 'Reactive Grout.' If they try to punch through that door, I want the mountain to hit them back with twice the force."
The grit of the aftermath was the labor of the "Cleaning Brigade." They had to enter the airlock in pressurized suits, moving the silent, broken forms of the ten infiltrators into the "Scrap Reclaimer." There was no ceremony. The Imperial clay on their boots was scraped off and analyzed for mineral content; their blackened iron beacon was dismantled for its silver circuitry.
Kael stood in the center of the command vault, the light of the arc-lamps casting long, jagged shadows against the iron ribs of the ceiling. He had reached a thousand, and he had lost them in the same breath. The mountain was heavier now, not just with iron, but with the reality of what it took to survive.
"We need to move the 'thousandth soul' celebration to the next week," Kael told Elms, who was still staring at the ink-smudged ledger. "And Elms? Increase the 'Steam-Triage' time to forty-eight hours. No one enters the inner vaults until we've mapped every inch of their skin. If the Empire wants to send us ghosts, we'll make sure they stay in the dark."
Kael began sketching the Piston-Gate—a massive, steam-driven hydraulic ram that would be installed behind the intake airlock. If the door was ever breached again, the ram would move forward with ten thousand tons of pressure, physically crushing the entire corridor and sealing the mountain forever.
The city was born in a vacuum, and as Kael looked at the flickering mercury pool, he knew the "Golden Finger" was already beginning to hum again. The Empire was bringing up the heavy siege-mortars. They were done with tunnels. They were going to try and crack the mountain like a nut.
"Proceed with the Tier 14 excavation," Kael said. "We need to go deeper. If they're going to pound the roof, we need to move the residential tiers below the basalt-line. We are leaving the limestone behind."