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"Morning."

"You objected."

"I did."

"Denied?"

"In under an hour."

"That's a good turnaround for a bureaucracy." She shoulders her pack. "Let's not waste it."

The service lift to Sublevel Twelve takes nine minutes. Twelve is restricted, which means the last surface engineer to see it without a Civil Authority escort did so before the Border Wars ended. The air down here runs cool and still and slightly wrong, the pressure differential sitting a half-percent under nominal because it has for as long as anyone has measured it.

I expect her to talk. She doesn't. She reads.

Forty meters into the primary gallery she stops at a valve cluster and crouches, and I let her, because I want to know how long it takes her to say something incorrect.

"Four-lobe actuator," she says. "That's pre-Border. They stopped making these after the second armistice — the four-lobe pattern had a torque problem in cold conditions and everybody switched to the six." She reaches out, doesn't touch it, traces the wear ridge on the arm with a fingertip held a centimeter off the metal. "This one's been rebuilt. Twice. Different hands both times. The second one didn't have the right shims, so they packed it."

All of that is accurate. It took me four years underground to learn to read a rebuild off an actuator arm.

"Who taught you that?"

"Nobody." She stands, brushing her palms off on her thighs. "Machines will tell you what happened to them. Most people just don't let them finish the sentence."

I do not have a reply to this, so I begin walking, and she falls in beside me without being asked.

We work the gallery for three hours. She is faster than she should be and she asks better questions than the last four specialists the Coalition sent me combined, and she reaches for things. Twice I have to tell her not to. The second time she pulls back and says, "Noted," without argument, and I revise my estimate of her downward on recklessness and upward on everything else.

It is on the return leg, in the connecting corridor between the gallery and the lift, that she stops walking.

"Wait."

I stop. "What."

"The water."

There is water in the corridor. Every corridor on Twelve has water in it, and I say so.

"On the way in, the seep was running down the left seam. I watched it for maybe ten seconds because it was making a nice little braid over the weld." She points with her chin. "It's on the right now."

"Seeps move."

"Seeps move when the load path moves." She is already backing up, one hand out behind her to find me. "Water goes where the structure lets it go. If it changed sides in three hours, something above us changed shape in three hours."

Nineteen years in these tunnels have given me a great many reasons to distrust a surface engineer's intuition. They have also given me an ear, and the corridor is quieter than it was.

"Out," I say. "Now."

We are eleven meters from the junction when the ceiling lets go.

Sound first, a low tearing that goes through the soles of my boots before it reaches my ears. Then dust. Then the weight of the world coming down behind us in sections, one after another, unhurried, the way old ferrocrete always falls.

I have her collar. She is moving anyway. Grit in my teeth. The lights strobe and die and the emergency strip flickers up in stuttering green, and we come out into the junction on our knees.

Silence, afterward. The particular silence of a space that has finished rearranging itself.

She coughs, spits, and looks back at the wall of rubble where the corridor used to be. Her breathing is fast and shallow and her hands shake — a normal response, correctly timed, and she does not pretend otherwise.