The first sign wasn't sound.
It was scent.
A bitter tang carried on recycled airflow—acrid, metallic, wrong.
Cael caught it while walking Grid Beta's outer rim. The air system should've filtered it. Should've neutralized anomalies.
But this wasn't mold.
Or fungal overgrowth.
This was burned stone.
"Grid sensors show no heat signature breaches," Nell reported, voice flat but alert.
Cael crouched and scraped a fingertip against the floor grating. A smear of soot marked the skin—fine, dry, old.
And fresh.
That contradiction set every hair on his neck on edge.
"Run airflow trails. Check vents C through F. Track particulates."
Nell nodded and disappeared into the network.
By the time Cael reached Vent D-3, the source wasn't a mystery.
It was teeth.
The tunnel was narrow, partially collapsed, half-forgotten. Not part of any active grid.
But someone had made it passable.
Not reinforced. Just… cleared.
Bones lined the edges. Charred. Cracked. Crushed.
The soot smell grew heavier as he stepped inside.
And there, on the wall just before the next bend—scratched in with something sharp:
|::|
A symbol he didn't recognize.
Two vertical lines, two colons between them. Repeated. Staggered. Deep.
He took a step closer—
And the tunnel growled.
Low. Mechanical. A sound built not for communication, but for warning.
He stepped back immediately and signaled for Nell.
"We've got something old. And alive."
"Alive?"
"Or programmed to make us think so."
Later, the planning chamber flickered with alerts.
Nell traced the tunnel markings to an old data set buried deep in the fragment logs—something from a long-expunged Vault.
"The structure matches partial patterns from Firebreed Subroutines," she said. "Architect-class deterrent constructs."
"Defense golems?"
"No. Not defense. Deterrent. Their design logic was based on psychological rejection. You don't fight them. You leave."
Cael frowned. "What are they guarding?"
"Unknown."
"What are they from?"
"No known Architect claims them. System lineage: Obscured."
Myla leaned against the console.
"Ash Teeth. That's what the Dust Cities called them. Things built in the early Sundering. Traps for thinkers. Bones for the bold."
"Sounds poetic," Riven muttered. "Also sounds like we shouldn't dig."
Lys folded her arms. "But someone already did. Or it wouldn't be awake."
The room went still.
Cael made the call.
Seal the tunnel.
Reinforce the air vent.
No probes. No intrusion.
Not yet.
"We don't poke unknown ghosts unless they knock first."
But that night, beneath the silence, one of the outer grid walls began to flicker.
Not breach.
Not break.
Just pulse—as if breathing.
And beside the wall, where soot had collected thick and black, someone etched the same symbol again.
|::|
No message.
Just presence.