Bram’s brass plate had been bolted to the wall for so long that the imprint of its edge remained in the mineral surface after he removed it. Whatever had occupied the missing second plate had left four small holes and a patch of cleaner metal on the back.
Elian held it beside his old map. “The movement mark is genuine. This line connects it to a ventilation symbol.”
“Can you tell where the line goes?” Iven asked.
“Not from this piece.”
“Then we find the rest.”
They were in the clinic, where Sera had insisted Bram stay while the cut on his leg was cleaned and bound. The worker had accepted the treatment but not the bed. He sat on a chair beside the table, holding a cup of broth and directing anyone who passed toward the lower junction.
“The gate needs a new catch,” he told Neri. “Iven closed it, but it won’t stay shut if the frame moves.”
“I’ll send someone.”
“Send two. The lower stair is slick.”
“You can choose them after you finish the broth,” Sera said.
He drank. Iven had learned that arguing with Sera while holding hot liquid was a poor way to preserve either the argument or the liquid.
Kesh had returned to the vent with Rysa’s crew at first light. They found the predator’s body caught against the far ledge, where the water narrowed beneath the bridge. Its broken forelimb and the damaged plates showed the marks of Iven’s strikes. It had no equipment, no graft, and no obvious connection to the pale guardians. Its stomach contained bird feathers and pieces of leather.
“A scavenger that learned to hunt,” Kesh said. “The workers call it a vent-hook. I don’t know how common it is.”
“Are there more?” Neri asked.
“We found tracks from at least one. We couldn’t tell whether they were all from this one.”
“That isn’t comforting.”
“It’s a reason to go prepared.”
The lower fan fed a drying room used by the clinic and several workshops. With it stopped, damp linen and filter cloth were accumulating faster than the workers could move them to other rooms. The upper station’s smaller vent had also lost blades, but it was a separate machine. Repairing the lower fan would restore the immediate flow and give them a chance to inspect the wall where Bram had found the plate.
Bram pointed to the diagram. “The missing piece was above this one. I could see the edge. The creature came out before I could loosen it.”
“Why did you take the first plate?” Elian asked.
“It had come loose. I thought it might fall into the valve.”
That made the discovery less mysterious and more useful. The plate had not been hidden in a special chamber waiting for a particular person. It had nearly fallen into a machine because its fasteners were old.
Neri unrolled a drawing of the collapsed bridge. “We can reach the far side from the lower junction. The near side needs support before anyone carries a fan across it.”
“Can we use the upper hatch?” Kesh asked.
“We can, but the animal’s duct opens near the bend. I’d rather keep that route as an exit.”
Iven examined the drawing. The lower junction connected to the far stair by a narrow passage. The stair itself had a service platform above the dark-water channel. If they brought the fan parts in from below, they would not have to cross the broken gap until it was braced.
“I’m going,” he said.
Sera looked up. “Your shoulder?”
“Bruised. I can lift the parts.”
“You can lift some of them.”
“Then I’ll let someone else feel useful.”
“I’m serious.”
“So am I.” He rotated the shoulder carefully. It hurt at the end of the movement, not at the beginning. “I won’t use it to catch a falling pipe.”
“That’s a strangely specific promise.”
“I like to set goals I can meet.”
They took a crew of six: Iven, Neri, Kesh, Lenn, a mechanic named Vela who knew the lower fan, and a rigger from Rysa’s cooperative. Sera remained at the clinic with Bram and the injured worker from the chamber. She supplied masks and a warning about the air: a stopped fan did not guarantee gas, but it removed a means of dispersing it. The crew carried a flame lamp and a small mechanical air indicator. Neither could detect every hazard.
They entered through the lower junction. The passage smelled of damp metal and old heat. Vela led them past a line of valves, each with a painted arrow showing the direction of flow. The paint had peeled from one arrow, leaving two red marks that could be read either way.
“That valve feeds the drying room,” she said. “Don’t turn it until I’ve checked the pressure.”
“I wasn’t going to,” Iven replied.
“You were looking at it.”
“I look at a great many things I don’t turn.”
“That’s reassuring.”
At the far stair, the water below the bridge moved steadily through the channel. The predator’s body had been removed to a netted ledge for Kesh’s examination. Iven did not look at it for long. The damaged forelimb was enough to confirm which creature it was.
The surviving bridge span had shifted when the pipe fell. Its far brackets remained attached, but one had bent. Neri’s crew fitted a temporary support beneath the span from the service platform. Iven held a plate brace under the bracket while the rigger set the first prop. The brace carried only a share of the load, and he released it as soon as the prop was secure.
“Can you lower the pipe?” Vela asked.
“Not until we know what it carries,” Neri said.
Vela traced it along the wall. “Warm air from the fan housing. The pipe is empty now.”
“Empty of flow, not necessarily pressure.”
Vela checked a gauge and opened a small test valve. Air escaped in a short hiss, then stopped. She left the test valve open while Jem’s replacement chain—brought by the rigger—was fixed to the pipe. They lowered it until the bridge rail was clear.
Iven crossed the remaining span to the wall where Bram had found the plate. The brass outline was visible above the valve. A second plate still hung above it, caught by one corroded screw. The screw head was worn almost smooth.
“Can you take it down without breaking it?” Elian had asked before they left.
“I can try.”
Iven set the spanner aside and used a narrow bit from Vela’s kit. He cut a fresh slot into the screw head, fitted a flat driver, and turned gently. The screw resisted, then moved. The plate came away into his hand.
A sound came from the duct above him: a rapid series of clicks, then a scrape.
“Kesh,” he said.
She was already looking up. A shadow moved behind the broken seam. It was too small for the dead predator and too fast for a tool caught in the air current. A second shadow followed it.
“Back to the stair,” she called.
The crew withdrew. Iven kept the plate against his chest and stepped backward along the bridge. The first creature dropped from the duct. It was about half the size of the one he had fought, with the same dark plates and hooked forelimbs. The second stayed above it, gripping the seam.
The young one landed on the bridge and rushed him.
Iven had plate, piston, and hook seated again. He met the rush with a brace angled down toward the bridge deck. The creature’s first hook struck and slid. He pushed the brace forward, forcing the animal’s head low, then stepped around its side and struck the shoulder joint with a piston impulse.
The blow drove it into the rail. The rail held. The creature recovered and sprang toward him a second time.
Kesh stood at the far stair with her pole ready. “Don’t let it pass you!”
“I wasn’t planning to.”
The second creature dropped from the duct behind the first. It landed awkwardly and turned toward the crew. Iven could not block both with one small brace. He cast the hook at a sound beam above the bridge and pulled himself sideways, crossing between the second creature and the stair. He released the tether, caught the handrail, and drove his shoulder into the animal’s path.
It hit him hard enough to move both of them. His bruised shoulder protested. He used the motion, turned, and sent the creature against the lowered pipe. It caught the pipe with one hook and tried to climb over.
The first creature came at his legs. Iven stepped onto the bridge rail, not with spring step but with an ordinary jump, and let the hook tether take some of his weight. The creature passed beneath him. He dropped behind it and struck the same shoulder joint again. This time the plate cracked.
The animal gave a low rattle and retreated into the arch. Its companion followed, dragging the damaged limb clear of the pipe. Neither returned immediately.
Kesh kept the pole pointed toward the duct. “Are they following?”
“Not yet.”
“Then don’t make them.”
Iven backed to the stair. The rigger closed the service gate after him and secured it with a temporary chain. The creatures could still use the duct, but the crew had time to reach the lower junction.
Vela counted the people. “Six.”
“Good,” Neri said. “We don’t go back until we’ve closed that seam.”
“Can we close it without trapping the animals inside?” Kesh asked.
“There’s another opening above the channel. If they use it, we can close the lower seam.”
“And if they don’t?”
“Then we choose whether to remove them. The fan can’t stay stopped forever.”
Kesh accepted that. She did not argue that the creatures should be allowed to hunt workers indefinitely. She wanted their choices understood before the crew made its own.
At the surface, Elian laid the second plate beside the first. Together they formed a narrow diagram of the ventilation line. The upper plate showed three branches and a series of marks beside one branch. The marks were not words, but the pattern matched a notation in the older route book: a place where a line met the outer armor and continued toward a fixed station.
“Fixed ground?” Iven asked.
“Possibly. The notation means a station outside the moving structure. It could be on another deck, a detached platform, or land.”
“Can we find the station?”
Elian turned the plate. A shallow groove ran along its edge. He traced it to a small circle near the bottom.
“The route book has a matching circle. It names a place called the Sill.”
Tavin, who had come to the clinic with a load of clean blankets, looked up. “Long Sill?”
“You know it?”
“I know a freight stop by that name. Fixed stone, warehouses, a crossing used when the convoy passes the escarpment.”
“Could it receive people?” Neri asked.
“A few, certainly. A city?” He shook his head. “I’ve never seen the ground above the warehouses.”
Iven looked at the paired plates. They did not prove there was room for everyone. They gave the question a direction and a place that someone could physically visit.
“Who runs the station?” he asked.
“Trade crews. Some live there year-round. Others come with the convoy.”
“Can you reach them?”
“I can send a message on the next freight line.”
“Ask about water, shelter, and the approach,” Asa said from the doorway. She had come to deliver food for Bram and the injured worker. “And ask what the people already there need. We can’t plan a refuge as if they’re empty rooms.”
Elian added the questions to his notebook. Tavin wrote a message for the freight captain. Neither called the Sill a solution yet.
Iven laid the plates together on the table. The lines crossed the metal, left one edge, and continued into a place he had never seen. Somewhere beyond Mercy’s moving body was fixed stone, with people who knew the ground and a station old enough to appear on a forgotten diagram.
He wanted to see it.