The convict swarm behind him didn't finish turning.
It started to.
Hands and eyes began to reorient toward the nearest bleeding things—toward Latch's wet cough and Mark's shoulder blood. But Mark had already pushed the wave backward into boots, already turned human hunger into a collision instead of a grip.
He didn't wait for the swarm to decide.
Decision time was stillness time.
Stillness killed.
He took the half-open grate at the choke.
Not because it was safe.
Because it was narrow.
Narrow spaces forced swarms to become lines, and lines could be outrun without sprinting if you kept your feet.
He shoved Latch through first.
Latch's injured knee hit the lip and buckled. The boy made a wet choking sound and tried to freeze in the moment his body decided it couldn't bend again.
Freeze was stillness.
Stillness was execution down here, because breath was already a limiter.
Mark yanked the collar chain—wrapped around his left wrist—using torso and hip line, not fingers. Fingers weren't reliable. The chain bit raw skin and sent wet stings up the arm.
He didn't stop to feel it.
He forced Latch forward.
Latch crawled.
Ugly.
Necessary.
Mark followed, pushing the falchion ahead flat, blade down, letting it scrape stone once—short, harsh—so his nervous system didn't name the crawl "hiding."
Hiding was calm.
Calm killed.
The duct took his helmet immediately.
The ceiling was too low.
Stone and metal pressed tight enough that the helmet scraped and then jammed against a narrowing brace. The brace didn't care about his head protection. It cared about clearance.
Mark didn't fight the brace.
He removed the helmet.
Not neatly.
Not with hands.
His right hand was cramping around the falchion handle and needed to keep a weapon ready. His left shoulder was failing and bleeding and couldn't handle a lift.
He used the bracer and forearm.
He hooked the helmet rim against the duct edge and shoved his head forward out of it, letting the helmet catch and hold for a beat. Then he reached back with his bracered forearm and dragged the helmet along behind him rather than leaving it. Leaving it would create a sound cue for pursuers to track, and losing protection mattered. Weight was protection.
The duct breathed heat.
Not open furnace heat.
Pipe heat.
A dry warmth that rose through metal ribs and made sweat immediate, turning damp cloth into slip again. The air was thinner here, moving through a narrow channel, and the smell was mineral and ash rather than rot.
Ash meant closer to furnace lanes.
Furnace lanes meant higher oxygen? Not necessarily.
It meant hotter air and tighter space.
Tighter space stole breath. Breath was the primary limiter now.
Mark's breath count shrank.
Inhale—one.
Exhale—one.
Not from panic.
From geometry.
The cracked rib punished each inhale as the stiff board at his belt pressed into it under the hunch. The courier tube jammed into the belt wrap pressed too. Hard cylinder, hard board, hard rib. The belt bulge was now a cage he carried inside his own skin.
His left shoulder smeared blood on the duct wall when it brushed. The shoulder joint slid once in the crawl and sent lightning down the arm. The forearm burn pulsed. The arm was weight, not tool.
One-arm traversal.
He couldn't climb with two.
He couldn't pull with two.
He had one reliable side for controlled movement—his right—because the left was failing and because the collar chain leash to Latch was anchored on the left wrist, turning the arm into tether rather than limb.
He adapted without thinking.
He became a three-point machine: right forearm and bracer as primary, knees as secondary, hook tool as third.
The hook tool—new leverage—was clipped into the collar chain link, giving him a right-side tow line so he didn't have to yank with the left shoulder.
He used the hook to pull Latch in short increments.
Hook.
Pull.
Slide.
Latch crawled ahead and then sagged, injured knee refusing to drag on hot metal for long. The boy's wet breathing filled the duct. Each cough stole oxygen and increased humidity, making the hot air feel thicker.
Mark didn't let Latch cough into stillness.
He kept Latch moving by tugging the chain in micro pulls, never allowing a full stop.
Micro movement was survival now.
Behind them, the convict swarm and boot line collided at the grate mouth.
A roar.
A clatter.
Then the sound changed—less chaotic, more determined.
Boots reasserting.
"Clear it—!"
"Down the run—!"
The duct hid them, but hiding was dangerous because it could feel like shelter, and shelter triggered drain. The engine didn't understand "duct." It understood "enclosed."
Mark made the duct hostile with sound.
He scraped the falchion flat along a metal rib—rasp—then lifted it. Not loud. Enough to keep his nervous system from naming this "quiet."
Quiet corners had already begun to steepen the drain even while he moved.
The heat increased.
The duct narrowed again and bent upward slightly, forcing a steeper crawl angle. The metal ribs under his palms were warmer. The wall seams were tighter. The air tasted dry and sharp, ash and iron.
Mark's breath count collapsed further.
Inhale—half.
Exhale—half.
Oxygen pinch.
Not just engine.
Physics.
The duct was stealing air by volume and by temperature, forcing shallow breaths that couldn't clear carbon dioxide properly. The body wanted to panic. Panic spent breath. Breath was life.
Mark refused panic by making danger external.
He could hear boots scraping into the grate behind now, one set at least. The duct amplified small sounds. A hook tool clinked. A man's breath came through cloth, close enough to be real.
Threat present.
Good.
Threat kept the engine from finishing him immediately even as the duct stole oxygen.
But heat spiked suddenly.
Not gradual.
A blast of hotter air rushing through the duct like a cough from the furnace system. The blast stole the next inhale by making the lungs feel already full, and it stung the throat with dry heat.
Mark's vision tunneled.
His fingertips tingled.
The ear ringing needle-thread sharpened into a loud line, drowning the duct's subtle sounds.
Heat spike / collapse risk.
Latch gagged ahead, a wet choking sound that threatened to stop him fully.
Stop would be death here.
Mark shoved forward with his right shoulder and forearm, using body mass to push Latch's torso and keep him sliding. Sliding was ugly, but sliding meant movement. Movement meant not dying in a duct.
His right hand cramped on the falchion handle and the handle rotated by a fraction.
Fraction became near-drop.
He trapped the handle against the bracer and forearm, using the bracer as a clamp jaw. His fingers were no longer the primary grip. Bone was.
His left wrist tether tugged hard as Latch's body snagged on a duct brace.
The chain bit raw skin.
The left shoulder tried to take load and slipped.
Lightning pain.
Breath hitched.
The engine tightened—drain flare—because the hitch threatened stillness.
Mark forced motion through it.
Inhale—one.
Exhale—one.
He had to clear Latch's snag before the duct heat spike finished them both.
He used the hook tool.
He reached forward with the hook, caught the brace edge, and levered Latch's cloth bundle and ankle chain line free without needing to lift with the failing left arm. The hook did the lifting. The right forearm did the pull.
Latch slid forward again.
The duct narrowed into a section where the metal ribs were visibly darker—heat staining—suggesting proximity to a furnace vent. The air was hotter, drier, and the duct's draft pulled hard in one direction like a lung inhaling.
That pull could help movement.
It could also steal balance.
Mark used it.
He stopped fighting the draft and let it carry their bodies forward in a controlled slide, using bracers and knees to steer and prevent a full uncontrolled slip.
Slide.
Steer.
Slide.
He kept the falchion flat, blade down, to avoid snagging.
He kept the collar chain taut enough to keep Latch ahead and moving.
He kept breath shallow, fast.
Inhale—one.
Exhale—one.
The pursuer behind scraped closer.
A metal tool clinked against duct rib.
A hook head? A gaff? A clamp? He couldn't tell in the ringing ear. He didn't need to. Any tool in a duct meant one thing: if they caught him here, he would not be held.
He would be stuck.
Stuck meant stillness.
Stillness meant drain.
Heat spike meant suffocation.
The convergence would kill fast.
Mark didn't wait to be caught.
He committed to the exit.
The duct ahead ended in a grate that wasn't bolted tight. It was a maintenance drop—hinged, meant to be opened from above and used to clean the duct.
Cooler air leaked around it.
Not clean.
Less hot.
More volume.
Mark shoved Latch into the grate first, forcing the boy's shoulders through. Latch's injured knee screamed as it had to bend. He hissed and nearly froze.
Mark yanked the collar chain and shoved again.
Latch dropped through.
Mark followed, letting the falchion slide through after him.
He fell less than a body length—controlled—into a narrow maintenance aisle.
Stone floor, damp, cooler than the duct. The air felt like a gift.
Gifts were poison.
The engine tried to misread the cooler air as relief and tightened.
Mark refused by making noise immediately.
He struck the falchion's flat once against the stone—clang—sharp in the tight aisle. Then he moved, pulling Latch forward, not allowing a single full breath to be taken as "rest."
Behind them, the duct grate slammed as the pursuer hit it.
Metal banged.
Not open yet.
But close.
Mark moved on.
Pain constant.
Shoulder failing.
Grip compromised.
Breath primary limiter.
And the surge windows—refills—were no longer comfort. They were borrowed function: brief alignments that let a ruined body behave like it still had two arms and full lungs.
He didn't have a refill now.
He had only motion.
So he moved, deeper into the maintenance aisle, toward whatever draft came next, knowing the duct had taught him the new rule with brutality:
Down here, the environment didn't just threaten to kill you.
It actively tried, and it didn't need hands to do it.