Linus dried his hands on a strip of boiled flax, though it did little for the sheep tallow. The grease supplied by the Interior merchants was always heavy on mutton fat; it smelled like an unwashed coat left out in the rain, and if a man let it sit in the valve seats past October, it turned the consistency of cold lard and seized the needle springs. He hated the smell enough that he kept three dried orange rinds in the watch pocket of his trousers. Every twenty minutes or so, when the vapor off the kerosene dip-tank grew thick enough to taste, he pressed a thumbnail into the rind to release the bitter oil and held it to his nose. It was an expensive habit, but Karanes had fruit carts from the south if you knew the carters, and Linus had spent six years making sure the carters’ wagon axles never threw a pin.
Around him, the south bay of the Karanes maintenance depot clattered with the steady, dull ironwork of an army trying to rebuild itself in three weeks.
Trost had cost them eighty-two sets of omni-directional mobility gear. Most had been retrieved as scrap: bent fan casings, shattered scabbards, and buckles sheared off by blunt impact. The men who had worn them were buried in lime pits near the river, but the steel came back here. Metal did not die. It merely lost its true.
Linus stood before bench four, scraping the rust from an anchor clutch with a three-cornered file.
"You’re filing against the temper," Moblit said. He didn't stop walking as he said it. Moblit was carrying a crate of regulator gaskets against his chest, his boots gray with stone dust from the courtyard. "If you take off the case-hardening, the wire will bite the groove."
"The groove already took a bite out of whoever owned it," Linus replied without looking up. He worked the file once more, feeling the rhythmic, dry *snick-snick* of hardened steel against slag-iron. "The clutch seized on the recoil. Look at the brass pawl. It didn't shear; it flattened. The boy was dropping toward the cobblestones and pulled the left trigger, and the spool just sat there. You want me to leave the burr so the next recruit gets the same ride?"
Moblit paused, the weight of the wooden crate shifting in his arms. He had dark semicircles under his eyes, bruised-looking and wet from lack of sleep. "Section Commander Hange wants the first three racks ready by midday tomorrow. Erwin’s quartermasters are signing for the draft horses at dawn."
"The horses can eat grass until noon. Steel takes the time steel takes."
"Don't let the Section Commander hear you say that."
"The Section Commander is currently on the roof of the stables trying to determine if horse dung burns hot enough to melt lead," Linus said. He laid the file down with a sharp *clink* on the lead plate. "I have ears, Moblit. I also have nostrils."
Moblit made a faint, exhausted sound in the back of his throat—neither a laugh nor a sigh—and moved on toward the parts crib.
Linus wiped his thumb against his apron and reached into the iron hopper at his left.
The hopper held the salvage from the third wagon that had arrived from the district depot at Stohess two nights ago. Officially, it was surplus stock: refurbished harnesses and pressure assemblies gathered from the reserve armories of Wall Sina to replenish the Survey Corps before the 57th Expedition. Unofficially, it was the bottom of the state barrel. The Central Military Police never sent anything to the outer walls that didn't have twenty years of dust on the oilcloth wrapping or a bent cylinder neck.
He pulled out a dual-spool drive casing.
It was heavy—heavier than standard issue by nearly half a pound. Linus lifted it with one wrist, testing the counter-balance. A standard Mark-IV housing cast from iron-bamboo alloy weighed four pounds, two ounces empty. This one felt like a cobbler’s last.
He set it on the bench anvil.
The housing had been dipped in black lacquer, fresh and sticky, covering the foundry crest on the flank. That was common enough; when the Wall Sina smiths took back field-worn units, they dipped them whole to seal out moisture before crating them for the long haul down the canal. But the dip was too thick around the spindle boss, pooling in the safety-wire holes. Someone had used an asphaltum base, the kind they used on bridge footings to hide cold cracks in the masonry.
Linus didn't like asphaltum. It smelled of sulfur, and it lied about the iron beneath it.
He took his paring chisel—a narrow, flat-ground tool he had made himself from a broken scabbard spring—and tapped the lacquer along the seam with a boxwood mallet.
The black enamel flaked away like dried scab.
Beneath it, the metal was clean. Too clean. It wasn't the dark, oily gray of the southern foundries, nor the pitted, brittle cast iron that came out of the civilian works near Trost. It had the faint blue iridescence of water-tempered steel from the deep vaults—the high-pressure stock reserved exclusively for the royal armory.
"Odd," he muttered.
The wall had rules for iron. Iron bamboo was mined under the supervision of the Ministry of the Interior; every billet was weighed at the pithead, logged into the district registry, and stamped with the triple-rose before it ever saw a forge hearth. A smith caught working unstamped bar stock lost his thumb. A smith caught selling high-pressure tubing outside the Wall Sina contract had his whole family relocated to the coal seams of the north.
Linus slipped the tip of his chisel into the retaining ring of the main drum. The retaining pin should have been soft copper—a shear pin designed to give way if the wire fouled inside the casing, preventing the spool from ripping the soldier’s hip joint out of the pelvis.
His chisel struck something that did not yield.
*Ting.*
The sound was clear and high, like a chapel bell rung across still water. It wasn't copper. It wasn't even brass.
Linus stopped. He looked around the workshop.
Across the dirt floor, two apprentices were arguing over a thread-die, their voices rising over the steady *thump-thump* of the treadle grindstone. In the far bay, Captain Moblit was shouting something through an open window toward the stable yard, his arms waving frantically as a plume of yellowish smoke billowed from the hayloft. Nobody was looking at bench four. Nobody was looking at him.
Linus picked up his magnifying loupe, mounted it into his right eye socket, and leaned down until his nose was an inch from the housing.
The retaining pin had been turned from solid tungsten-steel. More than that: it was threaded. Not the coarse five-pitch thread used by the Garrison workshops, but an impossibly fine, twenty-pitch spiral that required a jeweler’s screw-plate to cut. The head of the bolt was recessed, countersunk into the wall of the housing, and filled with lead flush to the curve of the cylinder.
Someone hadn't assembled this drum for field repair. Someone had sealed it to ensure it could never be opened with an armorer’s field kit.
*Therefore,* Linus thought, his mouth going slightly dry, *they didn't want the field armorers to see the drum.*
He did not call Moblit. Moblit was a good soldier, but Moblit had the unfortunate habit of writing things down in logs, and logs were read by logistics captains, and logistics captains reported to the supply commissaries who lived in the clean, dry mansions of Wall Sina.
Linus reached under his bench and pulled out his low-angle drift punch.
He seated the punch against the lead plug and tapped. Once. Twice. The lead deformed, mushrooming out of the recess in gray flakes. He cleared the shavings with his fingernail, exposed the twin slots in the bolt head, and took his split-blade key from the leather wrap behind his oilstones.
The bolt resisted. The threads were dry—no tallow, no graphite. It groaned, a minute screech of metal under tremendous torque, before it gave an eighth of a turn. Then another.
When the fastener cleared the casing, the end-plate did not pop off under the pressure of the internal spring.
Linus frowned. A standard retrieve-spring was six feet of coiled ribbon steel under thirty pounds of preload; the moment the retaining ring cleared the groove, the plate should have jumped across the bench. He had seen an apprentice lose three teeth to an untamed spring in the spring of ’48.
He wedged his blade under the lip and pried gently.
The plate lifted away without a sound.
There was no ribbon spring inside.
Instead, the interior cavity had been bored out, enlarged by six millimeters on either side, removing the reinforced structural ribbing that gave the casing its resistance to Titan-impact torque. The space was packed tightly with thin, circular leaves of parchment, each one cut to the exact diameter of the cylinder, like the wadding inside a field gun’s powder cartridge.
Linus sat very still.
The kerosene smoke drifted over him. He felt the cold draft that always came off the wall around sunset, sliding down through the depot’s high clerestory windows, smelling of damp limestone and horse sweat.
He reached in with a pair of watchmaker's tweezers and lifted the top disc of parchment.
It wasn't parchment. It was vellum—calfskin, white and smooth as milk, untouched by grease.
On the surface was an ink drawing, executed with a line so thin it looked like a spider had crawled across the skin after stepping in lampblack. It was a cross-section of an apparatus Linus did not recognize. It had two vertical reservoirs, a chamber with three nested valves, and an expansion nozzle that tapered to an opening no thicker than an embroidery needle.
Along the margin, written in a hand that was tiny, upright, and utterly devoid of the flourishes common to the district clerks, was a table of numbers.
*Atmospheres: 40. 60. 85. 110.*
Linus’s breath hitched.
Eighty-five atmospheres? The standard iron-bamboo canisters used by the Survey Corps held twenty-four atmospheres before the burst-discs ruptured. If you pushed twenty-six into them with the hand-compressors at the base of the wall, the seams wept oil; at thirty, the canister became an iron grenade that would take a soldier’s legs off at the hip. Nothing inside the walls could contain eighty atmospheres. The metallurgy didn't exist. If you put that much gas behind a spool, a man wouldn't just swing—he would outrun an arrow. He would tear his own spine out on the anchor release.
He lifted the second disc.
It was another diagram, but this one showed a boiler. Not the heavy, riveted steam-tanks they used to haul coal on the northern canal boats, but a cylindrical core surrounded by concentric coils, heated by a single, dark lump labeled with a symbol he had never seen: a circle pierced by three outward-pointing arrows.
Beneath the disc lay a small, rectangular object wrapped in oiled silk.
Linus lifted it out. The weight was concentrated, dense as a jeweler's ingot. He peeled the corner of the silk back with his calloused thumb.
It was a brass stamp—the kind used by the Interior Ministry to certify weapons for royal service. But where the three roses usually intertwined, the center of the crest had been gouged out with a cold chisel and replaced with an engraved letter:
*M.*
Not a Wall name. Not one of the families from the registries of the north or the south.
"Linus!"
He dropped his hand over the open casing instantly, his thumb jamming the parchment discs back into the cavity, his left palm sliding over the brass stamp until the cold metal bit into his skin.
Moblit stood in the doorway between the bays, wiping his face with a rag that was entirely black with charcoal. He looked wild, his cravat undone, his coat sleeve smoldering at the cuff.
"Moblit," Linus said. His voice sounded thin to his own ears. "Did she set the roof on fire?"
"The hay was wet," Moblit panted, his chest heaving. "It didn't burn. It just... it created a considerable volume of gas. She wants the high-pressure gauges. The ones from the Stohess crate."
Linus didn't move his hand from the bench. "They’re not calibrated yet."
"She doesn't care. She says she can smell sulfur in the horse manure and wants to test the expansion coefficient before the Commander calls the staff meeting." Moblit squinted through the dim light of the depot, looking at the tools scattered around bench four. His eyes lingered for a fraction of a second on the black flakes of asphaltum lacquer resting on the white anvil face.
"What's that?" Moblit asked.
"Old paint," Linus said. "Stohess sends us their garbage and expects us to polish it into silver."
Moblit looked at him. For four long seconds, the captain did not blink. His eyes, usually so hurried and bloodshot, settled on Linus’s shoulder with an odd, heavy gravity that Linus had never seen in the man before. It wasn't the look of a panicked adjutant trying to keep his superior officer from jumping into a pit of lime.
It was the look of a soldier who had spent six years counting the boots of dead men outside the gates.
"The Section Commander knows what came in that wagon, Linus," Moblit said softly. His voice didn't carry past the anvil. "She was the one who signed the manifest at the river gate while the MP escorts were looking the other way."
Linus kept his fingers clamped over the brass stamp. The edges were sharp; they were digging into the heel of his palm, right over the radial artery. He could feel his pulse knocking against the cold metal, regular and hard.
"She didn't sign for this," Linus said.
"No," Moblit agreed, his voice dropping another half-tone as he reached behind him to pull the workshop door half-shut against the yard. "She signed for eighty empty casings. If one of them wasn't empty, you’d better make sure it’s in your coat before she comes down from that ladder. She isn't the only one who has ears in Karanes."
He turned on his heel and walked back into the smoke, leaving the door unlatched, swinging slightly on its iron hinges in the gathering dusk.
Linus looked down at his bench.
The three orange rinds lay beside the boxwood mallet, shriveled and dry, their sharp fragrance entirely drowned by the cold, metallic stink of the high-tensile cylinder.
He did not put the retaining pin back in. He took the cylinder, wrapped it in his sheep-tallow flax rag, and dropped it into the leather tool-chest beneath his bench, right beside his spare socks and the whetstones his father had left him.
The iron didn't belong to the Survey Corps. It didn't belong to the King.
And looking out through the dusty window toward the inner gate—where the gray line of Wall Rose rose up until it cut the purple evening sky in half—Linus realized for the first time in his life that the wall wasn't just there to keep something out.
It was there to keep everyone inside from ever learning what an engine looked like.
***