The moment they stepped past the laser grid, the architecture of the facility underwent a violent shift.
The blinding, clinical white tiles vanished. The world turned dark and soft.
The floor beneath their boots changed to a thick, matte-black rubber that swallowed impact. The walls and ceiling were lined with dense, geometric foam pyramids, creating a suffocating texture that resembled the inside of a recording studio—or a padded coffin.
The air here was thick, viscous, and dead.
Sound didn't travel here; it died. The rustle of a coat, the intake of breath—every noise was instantly absorbed by the walls, leaving no echo.
"The Sonar Zone," Vance whispered.
He didn't speak with his vocal cords. He barely pushed air through his lips, shaping the words. Yet, in this oppressive silence, the friction of his breath sounded like a scream.
"From this point on," Vance gestured with a sharp movement of his hand, "speaking is suicide."
According to the intel extracted from Old Ghost, this sector was guarded by the "Echo" Active Sonar Array.
The empty air was not empty. It was filled with billions of high-frequency sound waves, screaming back and forth at speeds beyond human hearing. They bounced off objects, creating a real-time, millimeter-accurate 3D map in the central server's brain.
Here, optical camouflage was a joke. Blind spots did not exist. If you had mass, if you occupied space, you reflected sound. You were visible.
Unless you became a "Hole" in the world.
Vance looked at Cerberus and pointed to the black box on the boy's tactical belt.
Cerberus nodded. His hand hovered over the switch of the Low-Frequency Vibration Generator.
Click.
A hum, so deep it was felt in the bones rather than heard, began to radiate from them.
This device didn't silence them. It performed acoustic alchemy. It analyzed the incoming sonar pulses in real-time and emitted an inverse "negative wave" to cancel them out. Just as light meets light to create darkness, sound met sound to create absolute silence.
The moment it activated, Vance staggered.
A wave of violent nausea slammed into his gut. The inverted frequencies wreaked havoc on his inner ear's vestibular system. The world tilted sideways. Gravity seemed to dissolve. It felt like standing on the deck of a ship in a hurricane while completely motionless.
"Hold it together," Vance gritted his teeth, swallowing the bile rising in his throat. He signaled Cerberus to move.
Battery life: 14 minutes and counting.
They moved like ghosts across the rubber floor, fighting the urge to vomit with every step.
Just as they rounded a corner lined with black foam, the floor vibrated.
THUD... THUD...
It wasn't a footstep. It was the heavy, rhythmic crushing of rubber by something massive.
Vance's pupils constricted behind his sunglasses. He grabbed Cerberus by the shoulder and slammed him flat against the foam wall, merging with the shadows.
Seconds later, the monster rolled into view.
It was a "Warden" Class Sentry.
It had no legs, moving on silent, heavy-duty treads. It had no head, no optical cameras, no laser eyes. In place of a face, a massive, concave radar dish rotated slowly on a hydraulic neck, like a blind cyclops sniffing the air.
PING... PING...
The radar dish pulsed.
To a normal human, the scanner was silent. But to Vance, whose neural port was currently overclocked to translate all sensory data, the sound had a taste.
Copper.
Every time the invisible wave swept over his body, Vance tasted dirty, rusty pennies on his tongue. It was metallic, cold, and invasive.
The Warden stopped. It was five meters away.
The hydraulic neck hissed. The massive dish stopped rotating and swiveled directly toward the corner where Vance and Cerberus were pressed.
The taste of copper exploded into the taste of Battery Acid.
Vance's gums ached. The intensity of the sonar focus was so high it felt like electricity licking his teeth.
It suspects.
The invisible waves were washing over them, hammering against the vibration generator's shield, trying to find the solid matter beneath the acoustic cloak.
Cerberus's hand drifted slowly to his thigh, gripping the hilt of his tactical dagger. His muscles coiled, veins bulging on his neck.
If the generator failed—even for a microsecond—the machine would register their mass. The alarm would sound. Cerberus would have to launch himself, cover the five meters in 0.2 seconds, and drive the blade through the radar's central processor before the signal transmission completed.
Vance placed a hand on Cerberus's arm. He pressed down hard.
Don't. Move.
Vance stared at the faceless machine. Sweat rolled down his temple, dripping onto the rubber floor, instantly absorbed.
He watched the status light on Cerberus's belt. The red LED was flickering frantically. The generator was screaming silently, pushing its output to the redline to calculate the inverse waves for the focused beam.
It was an invisible arm-wrestle. One side was a military-grade sensor; the other was a black-market gadget held together by Old Ghost's soldering.
The Warden's processor whirred.
In its logic core, the data was contradictory. Its physical proximity sensors suggested an obstacle, but its sonar return showed a blur—a patch of "dead air" where a wall should be.
Logic Conflict.
Vance tasted blood in his mouth. The acid taste was overwhelming. Capillaries in his nose burst again under the sensory load.
One second. Two seconds. Three seconds.
Time stretched, distorted by the nausea and the adrenaline.
Finally, with a mechanical clunk, the Warden made a decision.
[Error Code 304: Acoustic Anomaly. Echo Absorption via Wall Degradation. Ignore.]
The massive radar dish turned away. The Warden engaged its treads, rumbling past them, heading down the adjacent corridor to hunt for clearer signals.
Only when the machine's taillights vanished into the gloom did Vance let the air out of his lungs.
He slid down the wall, gasping silently. The taste of acid faded, leaving a lingering, metallic bitterness.
"Too close," Vance mouthed, wiping fresh blood from his upper lip.
He checked the device on Cerberus's belt.
Battery: 35%. The standoff had drained nearly half their power.
Vance pulled up the retinal map. The red dot indicating their position had cleared the sonar maze. Ahead lay the final stretch before the central shaft.
But Vance's expression didn't lighten. It darkened.
"Don't celebrate yet," he signed to Cerberus, forcing himself to stand despite the lingering vertigo.
He pointed to the heavy blast door at the end of the hall.
"If this was the territory of the Blind, then ahead..."
Vance recalled the blueprints. The next corridor was fifty meters long. Perfectly straight.
"...is the Gravity Hall. Where even your own weight will betray you."