The Relay-Brain was clicking through its diagnostic cycles, and the Seismic Mirror showed the rhythmic jitter of the Imperial sonic bore, but for Kael, the true warning came from within. It was a cold, sharp needle of dread that pierced his consciousness—the familiar "Ping" of his innate danger sense. This wasn't a mechanical reading; it was the visceral certainty that the mountain's structural frequency was about to hit a "Critical Harmonic."
The Imperial engineers on the northern ridge weren't just drilling; they were searching for the mountain's natural resonant frequency. If they found it, the vibration would magnify until the iron ribs of the Tier 12 skeleton snapped like glass. Kael felt the warning intensify, a localized throbbing in his temples that pointed toward the Tier 11 Digester vaults. The Empire's sonic waves were focusing there, intending to rupture the methane tanks and turn the mountain into a furnace.
"We can't just brace the stone anymore," Kael shouted over the growing hum that was beginning to rattle the glass vials in the lab. "If we fight the vibration with rigidity, we break. We have to swallow it. We need the Acoustic Sink."
The grit of the project involved the immediate conversion of the Tier 11 "Sump-Galleries." Kael ordered the expansion brigades to flood the peripheral chambers surrounding the Digester with a non-Newtonian fluid—a thick mixture of fine limestone dust and recycled machine oil.
Unlike water, which would simply transmit the sound waves, this "Heavy Slurry" would act as a massive kinetic sponge. As the Imperial sonic bore struck the mountain, the vibration would be forced to move the viscous slurry, converting the destructive mechanical energy into harmless heat.
Socially, the mountain was in a state of "Silent Panic." The hum was now audible to everyone—a low, teeth-gritting drone that made it impossible to speak in normal tones. The population count stood at 990; ten souls away from the thousand-mark. The newest arrivals, sensing the mountain's distress, huddled in the residential tiers, their faith in Kael's "immortal stone" wavering.
A technical failure occurred when the Imperial bore shifted its frequency. The Internal Warning "pinged" again, a frantic, staccato pulse in Kael's mind. The "Heavy Slurry" in the North Sump was beginning to "Cavitate"—the vibration was so intense it was creating vacuum bubbles in the oil, which then collapsed with the force of small explosions, eroding the containment walls.
Kael utilized the "Mass-Tuning" bypass. He realized he needed to change the weight of the "Sponge." He ordered the foundry to dump three tons of "Scrap-Shot"—small iron pellets—directly into the slurry vats. This instantly changed the density of the sink, "de-tuning" it from the Imperial frequency and stopping the cavitation.
As the iron pellets settled, the internal "Ping" in Kael's head finally subsided into a dull ache. The mountain went quiet. On the surface, the Imperial sonic bore had likely seized, its energy reflected back into its own housing by the "Dead Wall" Kael had created.
Kael stood in the Tier 11 gallery, his boots covered in the gray oil-slurry. The immediate threat of collapse had passed, but the "Golden Finger" remained active, a low-level hum at the base of his skull. It wasn't over.
"They're not stopping, Elms," Kael said, wiping sweat from his brow. "The sink bought us time, but the warning hasn't cleared. It's moving. The threat isn't the vibration anymore. It's 'Infiltration.' They used the noise to mask something else."
He looked at the population log. A group of ten figures had just appeared at the white stone marker on the Seismic Mirror. The timing was too perfect.
"The count is 1,000," Elms whispered, unaware of the internal alarm still ringing in Kael's head. "We've done it, Baron. We are a city."
Kael stared at the ten newcomers on the screen. His internal warning spiked to a deafening roar. "Those aren't refugees. They're 'Sleeper Saboteurs.' They used the sonic bore to mask the sound of their own entry through a secondary vent. Don't open the intake gate."