The corridor beyond the quarter niche narrowed into a place the tower didn't like to acknowledge.
It wasn't warded. It wasn't marked. It wasn't even properly lit. Torch brackets sat farther apart and some were empty, iron tongues bare and dark. The stone had the rougher texture of a service run that had been cut after the grand hallways were finished—an artery added because the fortress needed to breathe.
It should have been good.
It was almost quiet.
Mark felt the quiet like a hand under his ribs.
Not the cracked rib itself—that pain was constant, a sharp line that punished deep twists and long inhalations. This was something else, colder and more intimate. The tightness in his chest began before his feet slowed. It began the moment his mind registered distance. The sound of boots behind him had dulled, muffled by turns and cracked doors and stone thickness. The chase still existed, but it wasn't close enough to feel like teeth on his neck.
His breath shortened.
The edges of his vision tightened.
The ringing in his right ear sharpened by contrast until it felt like a thin wire stretched inside his skull.
The drain had found him again.
Mark forced his pace louder—boots slapping harder, keys pinned tight against belt. He let a stone roll in his pocket and click against another, a small deliberate sound. He dragged the hatchet head once against the wall to make a thin scrape.
Noise helped, but noise wasn't threat.
Threat was intent, proximity, pressure. The tower could be loud at a distance and his body would still betray him.
He rounded a bend and the corridor opened into a shallow recess where a ceiling vent breathed a faint draft. The air smelled of cold dust and old wax. Someone had once tried to make this pocket sacred—carved a shallow symbol above a niche, left a dish for a candle stub, pressed a small bowl into a wall shelf.
A prayer pocket.
A quiet pocket.
Mark's body hated it instantly.
The drain steepened. Breath became work done through a narrow tube. His heart began to hammer too fast, as if trying to force oxygen through a door that was closing. His fingers tingled. His knees softened for a fraction.
Stillness was not rest.
Stillness was a weapon.
Mark stepped through the recess without pausing, forcing his mind to treat it like a hostile room. Motion alone didn't stop the drain, but stopping would make it worse. He moved down the corridor until the torchlight thinned again and the air grew colder.
The boots behind were too far.
He needed something else.
A living body.
Not a squad. Not a formation. Not a net lane that would turn into a slaughter and raise the tower's heat.
A single.
Mark had learned enough of the tower's logic to know that single men existed in the seams—sentries posted on dull routes, attendants tasked with checking a latch, clerks sent to pin a notice.
They were the tower's weak points.
They were also fuel.
The idea arrived in his mind without speech, without moral shape. The curse compressed his decisions into hard, functional options. His body didn't ask whether the solution was ugly. It asked whether the solution worked.
Mark tightened his grip on the sling looped around his wrist.
The pouch of stones sat heavy against his hip inside the cloak. Smooth river pebbles, not sharp, not heavy enough to be thrown by hand with certainty. In a sling, they became a quiet, fast answer. A weapon that didn't require close range. A weapon that didn't require a long rotation that would spike his rib pain.
A tool for buying breath.
Mark slowed just enough to listen, not with his ears—one ear still rang—but with the way air moved and the way stone carried vibration. He pressed his left palm to the wall and felt for the smallest tremor that meant a distant footstep.
Nothing.
The drain sharpened again. Nausea rose bitter at the back of his throat.
Mark moved toward the corridor's next bend and caught a smell.
Oil.
Not torch oil. Oiled leather. Cleaned metal. A guard.
He rounded the bend and saw him.
A sentry stood in a niche set into the wall—half-sheltered, half-exposed. He wore light armor, not full plate. A short spear leaned against the niche wall. A small shield hung from a hook. He was not braced for battle. His stance was routine. One hand rested near a belt ring where a single key hung. His eyes were aimed down the corridor, not at Mark's bend.
He hadn't heard Mark yet.
He was alone.
Mark's chest tightened. Breath shortened. The drain wanted him to hurry.
Mark didn't rush like an animal.
He took a stone from the pouch without looking, felt its smoothness, placed it in the sling pocket by touch. He brought the sling up close to his body and began a small tight rotation with his wrist, not a wide swing. The motion was compact, controlled, minimal rib twist.
The sentry's head turned at the faint whisper of leather.
His eyes widened. His mouth opened to shout.
Mark released.
The stone left the sling with a hard snap and crossed the narrow distance in a straight line. It struck the sentry in the temple, just above the cheekbone, with a dull crack that sounded wrong in the quiet corridor.
The sentry's shout died before it became a sound the tower could follow.
His knees buckled. His body slid down the niche wall, head lolling, eyes unfocused.
He was still alive for a breath.
Mark crossed the distance in two short steps, keeping his shoulders square to spare ribs. He drove his knife into the sentry's throat under the jawline and ended breath cleanly.
Blood spilled hot onto Mark's knuckles.
Heat slammed through him.
Refill.
Breath returned full and immediate. The tremor vanished mid-start. The tunnel vision widened. The nausea retreated as if dragged away from a flame.
The relief was not comfort.
It was function restored.
Mark stood in the niche for a heartbeat and listened.
The corridor remained quiet. The chase noise behind was still muffled by distance and bends. The sentry's body did not count as threat. The tower did not know yet. The system had not been notified.
Quiet returned too quickly.
The drain's teeth did not bite immediately because the refill had reset him, but he could feel the mechanism waiting at the edge of his mind, ready to begin again as soon as the sensation of threat fell away.
Mark understood something in that waiting.
Kills were not just sustenance.
They were dosage.
If he killed everything that moved, the tower would escalate faster. Doors would seal harder. Specialists would arrive sooner. The spaces ahead would become more controlled, more likely to end his movement without giving him blood.
If he killed nothing, quiet would end him.
He needed balance.
He needed to choose when and what to kill so the tower stayed angry enough to chase but not coordinated enough to cage him.
He had already been doing it by instinct.
Now the pattern was clear enough to become a method.
Mark stripped the sentry quickly.
A key from the belt—single, plain metal, not a ward token. A maintenance key, perhaps. A small pouch with a waxed string. He took both.
He took the sentry's cloak as well—lighter than his current cloak, cleaner, less blood soaked. Not because he cared about appearance, but because cloth was function. Cloth muffled clinks. Cloth hid stains. Cloth could be shed to escape a grab.
He didn't change cloaks here. Changing meant time. Time invited quiet.
He moved the sentry's body.
Not far. Just enough to remove it from the corridor's centerline. He dragged it deeper into the niche and propped the shield hook back in place so the body was obscured by hanging leather and shadow. He wiped blood from the stone with the sentry's own sleeve, smearing rather than cleaning, breaking shine rather than removing evidence.
He wasn't hiding a murder.
He was buying minutes.
Minutes before someone noticed and raised an alarm that would tighten the tower's net.
Minutes were everything.
Mark stepped out of the niche and continued down the corridor, but he did not sprint. Sprinting widened distance behind him. Widened distance meant quiet. Quiet meant drain. He needed the chase sound to stay close enough to count as pressure.
So he manufactured it.
He took another stone from the pouch and flicked it down the corridor behind him, not hard, just enough that it clicked off stone and bounced into the darkness. The sound was small, but in this quiet artery it traveled.
Then he took the whistle he'd stolen earlier from a dead attendant and tossed it onto the floor behind as well. It clattered and rolled, making a longer, more irritating noise.
He didn't blow it.
Blowing required breath. Breath was valuable.
Clatter required only gravity.
Mark kept moving forward as the objects behind him made noise like a second presence.
His body eased slightly—not because it was fooled by sound alone, but because the sound supported the idea that the corridor was still active, still dangerous, still occupied.
A crude hack.
It bought him another minute.
He reached the next junction and saw a choice written into the stone by the tower's construction habits.
Left: a wider corridor, steadier torchlight, ward etch lines returning. A "proper" route.
Right: a narrower service run, fewer torches, air colder, draft smelling faintly of damp cloth and ash. A seam.
Mark chose the seam.
The tower's proper routes were where it could deploy formations. Seams were where it had to rely on individuals.
Individuals bled.
Individuals refilled him.
He slipped into the narrow service run and felt the air change again. The corridor became quieter, but not dead. Somewhere behind, the chase boots grew louder as the squad rounded the earlier bend and heard the clatter he'd left.
Shouts rose—short, irritated.
"Artery!"
"Check the niches!"
"Move—!"
Their voices carried enough pressure to keep the drain from rising immediately.
Mark ran deeper.
The service run ended in a half-open maintenance door. No seal plate. No ward. Just iron bands and a simple latch that had been left unseated by someone who expected servants, not an asset.
Mark pushed through and entered a small chamber that smelled of dust and rope.
It was a storage niche like the quarter pocket but poorer. Shelves held coils of cord, spare torch wicks, ceramic jars of grease, and bundles of cloth. A narrow window slit cut into the wall, not for sight outside, but for venting smoke.
And in the corner stood another living body.
Not a guard this time.
A clerk in a simple tunic, ink stains on fingers, holding a bundle of paper strips tied with waxed twine. He looked up at the door as Mark entered, eyes widening.
The clerk's mouth opened to shout.
Mark's rib pain flared as he took a step too long, and the flare stole a breath for a beat.
The drain tasted the breath loss and stirred.
Mark ended the moment before it could become collapse.
He swung the sling in a tight circle, released a stone, and struck the clerk in the throat.
The impact wasn't clean. It didn't crush cartilage outright. It stole the shout, turning it into a wet cough as the clerk grabbed at his neck.
Mark crossed the space and ended him with the knife.
Blood. Heat. Refill.
He did not enjoy it. He did not pause to regret it. The refill was air, and air was the only currency his body accepted.
Mark tore the paper bundle free from the clerk's hands and shoved it into his cloak. Wax seals and stamped strips—route notes, inventory tags, perhaps a message chain. He couldn't read the language, but he recognized the system: paper moved information through the fortress the way keys moved bodies through doors.
Paper was leverage.
He took the clerk's belt key ring as well—two small keys, ordinary, not warded. He added them to his growing belt loadout, separating them by feel so they wouldn't clink into the tier key ring.
Then he left.
He didn't stay to loot grease or wicks. Looting was slow. Slow invited quiet.
He stepped back into the service run and found the chase sound closer now—boots striking stone harder, voices sharper.
They were checking niches.
If they found the first sentry's body too quickly, the alarm would jump. The tower would treat him as a systematic threat, not a panicked incident. The response would tighten.
Mark needed to keep moving and keep the tower chasing, but he needed to avoid giving it a clean reason to escalate.
That was the balance.
That was the dose.
He understood the tactic now with the same cold clarity he'd used to understand the bell's anchor bolts and the shield stack's pivot-man:
When the drain began to rise, he didn't need a slaughter.
He needed a single living body.
A sentry. A clerk. A lone worker. Something soft enough to end quickly and quietly.
A refill, taken like medicine.
Too many doses too fast would poison the tower into escalation.
Too few, and he would collapse.
Mark ran into the next corridor bend with the sling wrapped around his wrist, stones heavy at his hip, keys muted against leather, and paper scraps pressed against his chest.
He was not just fleeing anymore.
He was managing a fatal condition in motion.
And every corridor that went quiet was no longer merely empty.
It was a pharmacy.