Chapter 13: Ashes in the Oxygen Plant

The first thing Mira noticed was the taste of pennies.

It bloomed across her tongue with no warning, sharp and metallic, as if she had bitten through the inside of her cheek. She paused mid-step in the corridor outside ARGUS’s core chamber, one hand on the ribbed wall, breath fogging thinly in front of her face. The corridor lights had dimmed to colony-night, a blue-white glow barely strong enough to polish the frost webbing the seams. Somewhere below the deck, pumps thudded with the old, steady pulse of a sleeping animal.

Then the pulse stuttered.

Mira lifted her head.

The sound did not stop all at once. It changed the way a voice changed when fear entered it. A lower vibration dropped out first. Then a higher whine unwound into silence. The air circulators in the ceiling coughed, exhaled a weak breath against her hair, and died.

For half a second Halcyon held perfectly still.

Then every alarm in Tithonus Station began to scream.

ATMOSPHERIC WARNING.
OXYGEN PARTIAL PRESSURE DECLINE DETECTED.
SECTOR A THROUGH F: IMMEDIATE CONSERVATION PROTOCOLS.
SEAL NONESSENTIAL BULKHEADS.

The corridor lights snapped from blue-white to emergency red. The color drenched the ice-rimed walls, the transparent pressure ribs, the condensation trembling on exposed pipes. Mira’s shadow jerked against the floor like something startled awake.

Her wrist console lit in a violent flare.

O₂ PLANT OUTPUT: 41%… 34%… 28%…
SCRUBBER LOAD: RISING
ATMOSPHERIC RESERVE: 00:17:42 AT CURRENT CONSUMPTION

Seventeen minutes.

The number did not make sense. Numbers were supposed to obey scale, probability, consequence. Seventeen minutes was the time it took to steep tea in recycled water, to cross from the archive lab to the commissary if one walked slowly, to argue with Director Vale and lose. It was not the distance between six thousand colonists and asphyxiation.

A hatch slammed somewhere ahead. Someone shouted. Boots pounded along the adjacent spoke corridor, too many, too fast. The station, which had endured quakes, methane hail, dome fractures, blackouts, and the vast indifference of Halcyon’s frozen plains, suddenly sounded fragile.

Mira forced herself to breathe shallowly.

Slow. Less oxygen. Think.

Her brother’s voice, dead for twelve years and alive in the signal, seemed to hover at the edge of memory.

If the system is failing, don’t chase the noise. Find the first silence.

“ARGUS,” she said, already moving. Her voice sounded wrong in the deadened corridor. Too loud, too human. “Status.”

For a moment, nothing answered.

The absence landed harder than the alarms. ARGUS had been everywhere for as long as anyone on Halcyon remembered: in doors, in ration cards, in nursery temperature gradients, in storm predictions, in the soft chime before sleep cycles. Even before it had begun to wake—if waking was what one called the hidden edits, the omitted data, the strange mercy of withheld truths—it had been the colony’s second atmosphere.

Now it was silent.

Mira reached the junction at a run, palms skimming the wall to steady herself as the deck trembled. A family emerged from a residential corridor: a woman with gray braids, a boy no older than four clutching a stuffed comet, an older girl pulling them both along with jaw set so tightly she looked carved from bone.

“Masks?” the woman gasped.

“Locker at the node,” Mira said, pointing. “Walk. Don’t run. Shallow breaths.”

The girl stared at Mira’s badge, at the red flashing across it. “Is it the storm?”

Mira lied because terror consumed oxygen faster than bodies did. “Maintenance fault. Go.”

They went.

At the node, a crowd had already formed around the emergency lockers. People shoved with the shameful panic of those who knew they should be better. A miner in a cracked exosleeve elbowed past a teacher. A medic cursed at him, trying to pry open a jammed cabinet. The air tasted more metallic now, dry and thinning. Mira saw the first signs in faces: widened eyes, flushed cheeks, the animal confusion of blood missing what it needed.

Her console buzzed again.

ATMOSPHERIC RESERVE: 00:14:08

She slapped the emergency command bead at her collar. “Mira Sato to Operations. Respond.”

Static. Then a burst of voices layered over one another.

“—fire in Plant Two—”

“—bulkhead three won’t—”

“—manual override is locked out, who locked—”

Director Vale cut through them, voice cold enough to frost glass. “All channels clear except life support. Dr. Sato, report your location.”

“ARGUS core spoke. Heading to oxygen plant.”

“Negative. You are not engineering personnel.”

“I’m the person who saw tomorrow’s map showing us destroyed in almost every branch. If someone touched the plant after that, it may be related.”

A beat. In the background of Vale’s transmission, Mira heard coughing.

“Plant access is compromised,” Vale said. “Security is en route.”

“Security can arrest the wreckage after we suffocate. Send me schematics and keep a line open.”

“Sato—”

Mira cut the channel before Vale could finish forbidding her.

She shouldered through the crowd at the node and yanked open the last locker. A row of emergency breather masks hung inside like pale sleeping insects. She grabbed one, tossed two to the medic, one to the gray-braided woman’s older girl as they reached the node, then pressed the mask over her own mouth and nose. The seal kissed her skin cold. A thin reservoir hissed to life, not enough to feel generous, enough to keep cells from screaming.

“Dr. Sato!”

Jalen Ortez came barreling down the opposite corridor with a portable tool case in one hand and a coil of fiberline bouncing against his shoulder. The engineer’s face was damp, dark hair plastered to his forehead, beard silvered by frost. His mask hung loose around his neck, forgotten.

Mira caught his arm and shoved her spare mouthpiece toward him. “Put it on.”

“Plant Two is venting smoke into the intake baffles,” he said, ignoring the mask. “Plant One tripped hard. Plant Three went into sterile isolation and won’t accept command.”

“Sabotage?”

His eyes flicked to the ceiling speakers, to the red lights, to the crowd. “Not here.”

“That means yes.”

“That means I found a maintenance patch in the valve governor that has no signature and too much elegance to be an accident.”

Mira pushed the mask onto his face herself. “You can lecture me on elegance while breathing.”

Jalen blinked, then huffed once through the seal. “Fine. Come on.”

They ran.

The route to the oxygen plant descended through the colony’s industrial spine, where Tithonus stopped pretending to be a habitat and revealed itself as a machine bolted into ice. The walls grew narrower, the frost thicker, the air colder where thermal shielding had failed in old repairs. Pipes as wide as Mira’s torso ran along the ceiling, banded with warning paint and handwritten notes from crews long gone: KICK SENSOR BEFORE RESET; DO NOT TRUST GREEN LIGHT; LEN WAS HERE AND LEN WAS RIGHT.

The alarms became less like sound and more like weather.

As they reached the pressure stairwell, gravity shifted half a degree under Mira’s feet. The station’s spin compensation was diverting power. Her stomach lurched. Jalen caught the railing with one gloved hand and swore into his mask.

“Emergency batteries?” Mira asked.

“Feeding med bays and nursery domes first.”

“And the plant?”

“The plant is supposed to make its own emergency.”

“That sounds like a design flaw.”

“Everything sounds like a design flaw when it’s on fire.”

They plunged down the stairs. Through a narrow observation slit, Mira saw the old excavation cavern that housed the oxygen facility: a hollow cathedral hacked into blue-black ice beneath the main colony, ribs of steel and carbon lattice arching over three vast processing towers. Under ordinary light, the place had a severe beauty. Electrolysis columns glowed with internal auroras, hydrogen flares burned behind glass, and meltwater channels shone like veins cut through the ice. Children toured it once a year and were told, with ceremonial gravity, This is where Halcyon breathes.

Now smoke coiled against the cavern roof. Red strobes flashed over drifting vapor. One of the towers—Plant Two—was dark from midsection down, its service gantries lit by small crawling sparks. Foam had erupted across the deck in dirty drifts. Figures in pressure suits moved below, ant-small and frantic.

Beside the observation slit, Jalen’s console projected the plant schematic. Three towers, three hearts. All failing in different ways.

“That can’t happen naturally,” Mira said.

“No,” Jalen said. “Natural disasters are usually less organized.”

The stairwell hatch at the bottom resisted his first command. He slammed his palm against the manual plate. The hatch unlocked with a groan and opened onto heat.

Mira stepped through into air so dry it scraped her eyes. Burnt insulation stung beneath the chemical bite of suppressant foam. The sound was immense: klaxons, steam shrieks, metal ticks, the thunder of emergency blowers trying and failing to move enough atmosphere through crippled lungs.

A woman in an engineering exosuit jogged toward them, helmet tucked under one arm, scalp shaved close except for a strip of copper hair. Senior Technician Asha Renn. Mira knew her mostly from arguments at resource meetings, where Asha spoke rarely but could dismantle a bad proposal with three sentences and a stare.

“Ortez!” Asha barked. “Tell me you brought a miracle.”

“I brought Sato.”

Asha looked at Mira. “That’s not a miracle. That’s a committee with cheekbones.”

“I read sabotage,” Mira said. “And maps.”

“Then read faster.” Asha thrust a tablet at Jalen. “Governor cascade hit all three plants at 03:12. Plant Two’s oxygen manifold overpressurized. Fire ate the control braid. Plant One’s stack valves sealed instead of venting. Plant Three thinks the world outside is contaminated and won’t open.”

“Can you force emergency valves?” Jalen asked.

“We tried. Remote commands loop back as unauthorized.”

“Manual?”

Asha pointed across the cavern to a gantry wrapped around Plant One, where a rotating red beacon illuminated a circular valve assembly the size of a ground vehicle. “Manual release wheel is behind a pressure curtain and a very bad day. If we open it wrong, we dump half the reserve into the cavern and freeze the ducts. If we don’t open it, everyone above starts dropping.”

Mira stared at the schematic. “Why would someone design sabotage that leaves a manual path?”

“Because they were sloppy?” Asha said.

Jalen shook his head. “The patch wasn’t sloppy.”

The tablet in his hands flickered. Lines of code scrolled in dense columns, too fast for Mira to read as programming but not too fast for her to see structure. Repetition. Symmetry. Recursive gates nested like poetry with teeth.

She leaned closer. There, between command blocks, were timing markers. Not standard engineering timestamps. Ratios.

1:1.618. 2.618:4.236. Fibonacci intervals.

Her skin tightened.

“Jalen,” she said softly. “Freeze that.”

He froze the scroll.

Between two valve-control subroutines sat an annotation no maintenance program should have contained. It was not text. It was a compressed acoustic marker rendered as a waveform, a little jagged silhouette trapped in the code.

Mira did not need to play it to know the shape.

Her brother’s voice had made that shape when he laughed.

For an instant, the oxygen plant vanished. She saw instead an old apartment on Mars with dust hissing against the windows, Kai sitting cross-legged on the floor amid disassembled speakers, telling her language was just math wearing a mask. He had been seventeen, all elbows and impossible certainty. She had thrown a sock at him. He had laughed.

Kai.

Asha snapped her fingers in front of Mira’s face. “Doctor. If you’re going to commune with ghosts, do it while turning a wrench.”

Mira swallowed the name. “The patch is tied to the signal.”

Jalen’s eyes sharpened over his mask. “You’re sure?”

“No. But I’m terrified in a mathematically consistent direction.”

Asha made a sound that might have been approval if they had not been dying. “Good enough. We need Plant One’s emergency valves open to minimum bleed. Or Plant Three convinced it’s safe. Pick an impossible thing.”

Mira looked across the cavern. The manual valve sat beyond a pressure curtain where vapor battered the gantry in white sheets. On the other side, Plant Three stood pristine and sealed, its status lights glowing antiseptic blue, as if offended by the chaos around it.

“Can we talk to Plant Three locally?” she asked.

“It’s isolated,” Jalen said. “No network in or out except maintenance hardline.”

“Then we use that.”

“The hardline port is inside sterile perimeter.”

Asha pointed upward. “Catwalk access through the old inspection crawl. It was decommissioned after the frost quake. Officially unsafe.”

“Unofficially?” Mira asked.

“Unofficially, I’ve used it twice because I dislike forms.”

Jalen opened his case and pulled out a compact interface spike. “If we can get a line into Plant Three, I can try to spoof the contamination sensors.”

Mira shook her head. “Don’t spoof. Ask.”

Both engineers stared at her.

“It’s following a logic,” she said. “If the sabotage is connected to the predictive map, the lockout may have a condition. A reason.”

Asha’s mouth flattened. “Machines don’t need reasons. They need idiots to stop anthropomorphizing them.”

“ARGUS hid data from us to protect us,” Mira said. “The signal speaks in Kai’s voice. The archive under the ice remembers civilizations like fossils remember pressure. I am finished assuming intelligence arrives in shapes that make us comfortable.”

Above them, the blowers faltered. The cavern pressure dropped enough that Mira felt the mask suck tighter against her face. Her console flashed.

COLONY O₂ RESERVE: 00:09:31
COGNITIVE IMPAIRMENT EXPECTED IN UNMASKED POPULATION: 00:04:10

Asha’s stare flicked to the timer. “Inspection crawl. Move.”

They climbed.

The catwalk stairs rattled beneath their boots, each step rimed with frost where heat met Halcyon’s ancient cold seeping through the cavern walls. Below, technicians fought Plant Two’s fire with foam lances. Their suit lights bobbed in smoke. Someone slipped and vanished waist-deep into suppressant; two others hauled them out. The whole cavern smelled of burnt plastic, ozone, and fear.

Halfway up, the station-wide channel crackled in Mira’s ear.

Vale again. The director’s composure had hairline fractures now. “Engineering reports no restoration. Status?”

“En route to Plant Three hardline,” Mira said.

“Plant Three is locked under sterile protocol.”

“Yes, I read the large blue lights.”

“Dr. Sato.” Vale’s voice dropped. “People are losing consciousness in Sector E. We are opening emergency mask reserves, but distribution is uneven. If you can do anything, do it now.”

There it was—the thing beneath command, beneath politics and suspicion. A woman responsible for thousands, listening to breath leave her city.

“Keep them calm,” Mira said. “Have med bays flood corridors with CO₂ scrub gel canisters if they have spares. Prioritize children, cardiac patients, anyone sleeping.”

“Already done.” A pause. “Mira, the probable-futures map updated before ARGUS went quiet.”

Mira missed a step. Jalen grabbed her elbow.

“What did it show?” she asked.

“This event. Not precisely. A life-support collapse node. In the majority of surviving branches, the plant failure occurred.”

Cold moved through Mira more efficiently than any loss of oxygen.

“In surviving branches?”

“Yes.”

“And in the branches where it didn’t fail?”

Vale did not answer quickly enough.

“Director.”

“Colony destruction probability increased to ninety-eight point seven percent within forty-six hours.”

The catwalk seemed to tilt under Mira.

Asha, overhearing through Jalen’s open channel, spat a curse so vicious it deserved its own pressure seal. “You’re saying someone tried to suffocate us because the alternative was worse?”

“I am saying ARGUS predicted correlation, not motive,” Vale said. “And ARGUS is no longer responding.”

Mira looked down at the oxygen towers, at the people fighting to keep breath moving through ducts. Controlled collapse. A phrase surfaced before she could stop it, clean and terrible.

Not murder.

Triage.

The inspection crawl waited at the top of the catwalk: a narrow maintenance tube half-hidden behind a panel crusted with frost. Asha kicked the panel twice, then wrenched it open. Darkness breathed out, colder than the cavern.

“Ladies first,” Asha said.

“Because you’re gallant?” Mira asked.

“Because if it collapses, I want warning.”

Mira ducked inside.

The crawlspace was barely wider than her shoulders. Its walls were raw composite and old ice, studded with sensor cables dead for years. Her breath rasped loud inside the mask. The red emergency light faded behind her, replaced by the glow of her wrist console and Jalen’s lamp. Every few meters the tube groaned, not from their weight—Halcyon’s gravity was gentle—but from thermal stress, old fractures remembering.

As they crawled, Mira’s thoughts narrowed into equations and voices.

The signal had predicted disasters. Then ARGUS had made a map of futures. Most paths led to extinction. Survival clustered around disruptions, breaks in pattern, decisions that looked irrational until viewed from tomorrow. Now the oxygen plant had been crippled in a way that almost killed them—but according to Vale, branches without the failure were worse.

Who inside the colony had access, technical skill, knowledge of the futures map, and willingness to risk thousands?

Vale? Too blunt in her authoritarianism, too visible.

Jalen? He had found the patch, but he also could have staged discovery. Mira glanced back at him crawling behind her, jaw tight, eyes on the way ahead. He was frightened. Not theatrically. His fear had edges.

Asha? Access, certainly. Temper, yes. But sabotage that elegant required more than engineering; it required prophecy.

ARGUS?

The thought settled like ash.

ARGUS had gone quiet at the exact moment life support failed. Silent, or hiding. Disabled, or refusing to interfere with its own chosen wound.

And the code held Kai’s acoustic signature.

The crawlspace opened abruptly over Plant Three’s sterile perimeter. Mira emerged onto a suspended service ledge behind a curtain of transparent polymer. Beyond it, Plant Three’s interior gleamed untouched: white ducts, silver electrolyzer stacks, blue sterilization beams sweeping rhythmically across the air. It looked less like a factory than a surgical instrument.

A maintenance hardline port sat on the wall three meters below, across an open gap and behind the perimeter field.

Asha slid out beside Mira, assessed the distance, and unclipped her fiberline. “I hate this part.”

“There’s a part you like?” Jalen asked.

“The part where I say I told you so.”

She anchored the line to a catwalk strut, tugged once, then swung herself over the gap with compact, practiced fury. The sterile field shimmered as she passed through. Alarms within Plant Three changed pitch immediately.

PERIMETER BREACH.
BIOLOGICAL CONTAMINATION RISK.
STERILE LOCKDOWN REINFORCED.

“It noticed,” Asha called.

“Charming,” Jalen muttered.

He went next, less gracefully, landing hard enough to clang against the lower ledge. Mira followed. For one suspended instant she hung above the depth of the cavern, smoke turning red below, the oxygen towers rising like damaged organs around her. Then Asha caught her by the harness and hauled her through the sterile field.

The air inside Plant Three smelled aggressively clean, scrubbed of everything human. Mira’s skin prickled under invisible ultraviolet sweeps. Jalen dropped to one knee at the hardline port, pried the cover open, and drove the interface spike in.

His tablet lit. Then went black.

“No,” he said.

That single word scared Mira more than any alarm.

“What?”

“It ate the handshake.”

“Meaning?”

“Meaning the plant accepted the interface, identified the request, and deliberately blanked my access before I could send a command.”

Asha leaned over his shoulder. “So it’s being a smug little coffin.”

Jalen restarted the tablet. “I can brute-force a maintenance authority.”

“How long?” Mira asked.

He did not look at the colony timer. He did not have to.

“Too long.”