Luke slept lightly.
Not because he was afraid, but because underground sleep was never deep. Stone carried sound too well. Pressure changes traveled farther than footsteps. A distant scrape, a subtle vibration, a lamp flicker—any of it could pull you back to awareness.
When he woke, it was to the sound of water.
Not dripping.
Running.
Luke sat up at once.
The flow through the ceramic pipe near the corner sounded fuller than it had the night before. Too full. Water that rushed tended to do so right before it decided to go somewhere else.
He swung his legs off the mat and stood, careful not to wake Mira or Jorin. His father was already awake, sitting near the pipe with a hand pressed against the stone.
"You hear it too," Eren said quietly.
"Yes."
Eren frowned. "Pressure's wrong."
Luke moved beside him and placed his palm near the pipe joint. The stone vibrated faintly, a steady pulse that didn't match the normal rhythm.
"Upstream adjustment," Luke said after a moment. "Someone opened a valve too fast."
Eren exhaled slowly. "Water Handlers?"
"Or someone trying to be helpful."
That earned a dry huff from his father.
Eren stood and grabbed his boots. "Get dressed. We're checking the junction before breakfast."
Luke nodded and moved quickly.
By the time they reached the junction chamber, three other families were already there. A Water Handler knelt near the main valve, hands white with mineral residue, while two assistants stood ready with wedges and sealing paste.
"It surged," the handler muttered. "Didn't burst, though."
"Yet," Eren said.
The handler shot him a look but didn't argue.
Luke watched the wall.
Not the valve—the stone behind it.
Hairline cracks traced outward from the pipe's anchor point, faint but growing darker as moisture seeped into them. Luke crouched and pressed his thumb against one.
Cold.
Too cold.
"It'll split if you hold that pressure," Luke said quietly.
The handler glanced at him, irritation flickering across his face. "You again."
"I'm not saying now," Luke replied. "I'm saying soon."
Eren rested a hand on Luke's shoulder. "Lower it."
The handler hesitated, then twisted the valve a fraction. The rushing sound eased. The vibration softened.
A few people let out breaths they hadn't realized they were holding.
"Mark it," Luke added. "And reinforce from the west brace, not the south."
The handler opened his mouth to argue—then paused.
"…Why west?"
Luke hesitated. Too much explanation drew attention.
"The south stone's already tired," he said. "It's been taking load from Corridor Twelve for years."
Someone behind them muttered, "They're sealing Twelve tomorrow."
That settled it.
The handler grunted and reached for his chalk.
Luke stepped back and faded into the crowd as people dispersed, already shifting their routines around a problem that hadn't fully arrived yet.
That was how Hearth-Deep survived.
Breakfast was quiet.
Dried fungus, a small ration of root mash, water that tasted faintly of stone. Mira complained anyway.
"It's always the same," she said, poking at her bowl.
"That's the point," Jorin replied. "Same means alive."
Mira rolled her eyes. "You say that about everything."
"Because it's true," Jorin said.
Eren said nothing. He ate quickly, already mentally elsewhere.
"South route," he said once his bowl was empty. "We leave before mid-cycle."
Luke looked up. "I'm coming."
Eren studied him for a long moment. "You don't have to."
"I know."
"But you want to."
"Yes."
Eren nodded. That was all the permission Luke would ever get.
The south tunnels felt different today.
Not dangerous—just unsettled. The air was warmer, the drafts less predictable. Lamps here burned a little brighter, but their light seemed thinner, stretched.
The group was small. Eren. Two guards. The old pathfinder master—lean, sharp-eyed, his steps measured like each stone owed him an explanation.
Luke walked behind them, marking small details in his head. Scrape marks too high on the wall. Dust patterns disturbed and then resettled. A lamp cage bent inward as if struck from the side.
"Stop," the master said suddenly.
Everyone froze.
He crouched and brushed his fingers over the ground, then sniffed them. "Recent."
"Monster?" one guard asked.
"Movement," the master corrected. "Not hunting. Passing through."
Luke glanced down a side passage and felt that familiar pull in his gut—not fear, but misalignment. The stone there looked fine. Too fine.
"That way's unstable," Luke said quietly.
The master looked at him. "Why?"
Luke swallowed. "The supports don't match the ceiling stress. They were added later."
Eren frowned. "By us?"
"By someone trying to be fast," Luke said.
The master considered, then nodded. "We detour."
No argument.
They reached the southern observation point without incident. The damage there was subtle but undeniable—scratches along the stone where something large had brushed past, pressure marks where the tunnel walls had flexed.
"Migration confirmed," the master said. "We close this route after today."
One guard sighed. "Another shortcut gone."
"Shortcuts get you killed," Eren replied.
They turned back.
Halfway home, a tremor rolled through the stone—stronger than the one the day before. Lamps flickered. Dust rained down in thin sheets.
"Move," the master snapped.
They did.
The collapse wasn't catastrophic. Just a partial cave-in behind them, sealing a narrow side passage forever. The sound echoed for a long time.
Luke stared at the fallen stone.
"That wasn't on any map," he murmured.
The master's mouth twitched. "Maps are guesses that haven't failed yet."
By the time they returned, the town was already adjusting.
Corridor Twelve was being sealed earlier than planned. Tunnel Makers worked fast, wedging supports and packing stone with practiced efficiency. Light Keepers rerouted glow-moss beds to compensate for the darker paths.
No one panicked.
But everyone noticed.
Luke helped where he could—hauling wedges, carrying tools, passing messages. He said little. He didn't need to say much.
People remembered who had spoken before things broke.
That evening, Hearth-Deep gathered—not in celebration, but in quiet recalibration. Routes updated. Rations adjusted. Schedules shifted.
Someone asked if the surface trade would be delayed.
"Probably," came the answer.
No one complained.
At home, Mira sat cross-legged near the wall, carving small shapes into a piece of soft stone.
"What are you making?" Luke asked.
"A map," she said. "Of the places we're not allowed to go anymore."
Luke smiled faintly. "That'll be a big map."
"That's fine," she replied. "I like big maps."
Jorin lay back on his mat, staring at the ceiling. "Do you ever wonder," he said slowly, "what it's like up there?"
Luke knew what he meant.
"Yes," he said.
"Do you think it's better?"
Luke thought of the casing in his satchel. Of broken things that once worked beautifully. Of places that failed loudly instead of quietly.
"I think it's different," he said. "Different enough to be dangerous."
Jorin grunted. "Figures."
Later, when the lamps dimmed and the town settled into uneasy rest, Luke pulled the casing out again.
He didn't open it.
He just held it, feeling the weight, the precision, the history locked inside broken metal. Somewhere, someone had built this expecting it to last.
They'd been wrong.
Luke lay back and stared at the ceiling until sleep took him.
In his dreams, tunnels shifted. Routes closed. New ones opened, only to fail later. Everything moved in slow, inevitable patterns.
When he woke, his body felt rested.
His mind felt heavier.
The water was running steadily again.
For now.