He looked at the return lever, at the old brass scale he had rebuilt and rebuilt again in rooms that no longer seemed to belong to the same life. The old thrill was there, bright and shameful. Clean variables. A question made into motion. For one breath he hated that part of himself and trusted it all the same.

"Then you take the core and get out," he said. "If I'm not back almost at once, you go. No waiting. No heroics."

Mara's jaw tightened. "You don't get to tell me not to wait after this."

The chamber tone deepened. Somewhere behind the walls, a lock engaged with a heavy metal thunk.

Elias climbed onto the saddle. Pain flared under his ribs so sharply that he had to pause and set his teeth. He laid the satchel strap across his chest, checked the brake twice, set the interval wheel for a bounded run, and looked at Mara one last time.

"If it behaves," he said, "I will be back before the alarm cycles."

"If it behaves," Mara said, flat as stone, "you've still chosen the worst moment in the world to satisfy yourself."

He almost answered that it was not about satisfaction. The lie would have shamed them both. Instead he pushed the lever.

The chamber snapped away.