By the time she had slept, the frost had covered the floor.
She had not wanted to sleep. She had lain on the grating with her head on her bag and her eyes on the ceiling grille and listened to the hiss of the valve and the small ticks of the pipe, and she had thought about the school, and Nemi’s chalk squares, and the second column under next flight, and the widow’s pipe peeled open over the child’s bed. Then she had thought about nothing, and then Sera’s hand was on her shoulder, and four hours were gone.
They had slept in the lowest chamber, both of them, on the grating, on the red paint, because there was nowhere else to go; the lift would not rise without the keeper’s leave, and the keeper would not give leave until the valve was repaired, and Mara would not touch the valve tired, not after the widow’s pipe. She had told Sera so, and Sera had looked at her for a long moment through the visor and then sat down on the grating with her back to the cold wall and said, “Four hours. I’ll wake you.” She had not slept herself, as far as Mara could tell.
When Mara woke, the white crust around the leaking joint had grown. It had covered the collar entirely and crept down the pipe to the floor, and from there it had spread out across the floor plates in a fan, feathery white ridges running out over the black grating toward the middle of the room, as though the cold were reaching for them. Where it touched the grating, the grating ticked. Small sharp sounds, irregular, the metal contracting as the cold pulled heat out of it.
The pipe itself ticked louder. Each tick came with a faint shudder Mara could feel through her knees when she knelt in front of it.
“It’s worse,” she said. Her voice came out rough; the suit’s air was dry, and she had slept with her mouth open.
“It’s been worse for an hour,” Sera said. “I watched it.”
Mara looked at the gauge, still threaded onto the test port. Eighty-seven. Seven points down since she wrote the first number, and still falling.
The obvious thing was the collar. The leak was at the collar; the frost grew from the collar; the hiss came from the collar. A leak at a collar meant the collar was loose. In the yard she would have put a wrench on it and given it a quarter turn and the leak would have stopped. She had done it a hundred times. Her hand knew it before her head did.
She picked up Tavin’s wrench.
She fitted its jaws to the collar’s flats, under the frost, and set her grip, and began to lean into the handle.
The tone changed.
She heard it through the grating, through her knees, through the wrench’s handle in her hand: the pipe’s note, which had been a steady low hum under the hiss, dropped. The change was small. But the note went hollow, the way a cast bar goes hollow when you tap it at the crack, the way the grate bar at the repair stall in Gutter Lane had gone dull. A dead sound.
She stopped. She leaned no further. She held the wrench where it was, its jaws on the collar, not turning, and listened.
The hollow note held. As long as the wrench pressed on the collar, the note was hollow. She eased off, the smallest amount, and the note came back up a little toward where it had been.
She took the wrench away.
“What,” Sera said.
“Wait.”
Mara sat back on her heels. She took notebook II out of the sealed case, the one that was all procedure and diagrams, and opened it to a page she had looked at on the flight and not understood: a drawing of a valve like this one, cut in half, with arrows. A schematic. She laid it on the grating beside her and put her gloved finger on it.
The pressure came in here, through the pipe from the floor. It went up through the valve’s body. It met the seat here, a ring of softer metal that the valve’s plug closed against to stop the flow. Above the seat, holding the body together, the collar. The collar never touched the flow. The collar only clamped. The seat was where the flow stopped.
She traced it with her finger. In, up, seat, collar.
Then she looked at the real valve, at the collar under the frost, and she saw what she had been about to do.
She took the wrench and fitted it again, very lightly, not to turn but to feel. The collar would not move at all. It was tight. It was beyond tight. Whoever had last worked on this valve, the last smith, or some earlier visitor, or a machine, had tightened that collar past its range, so hard that the threads had begun to strain, and the collar was pressing down on the body below it so hard that it had begun to distort it. And beneath the collar, in the body, the seat had cracked.
That was the leak. A cracked seat, under a collar someone had already tried to fix by tightening, and tightened, and tightened again, every turn making it worse. If she had leaned on the wrench, she would have cracked the body itself. The pipe would have split, and whatever was in it would have come out all at once, cold from the dark side of a sun, onto her knees on the grating.
She sat with her hands on her thighs.
Clean the surface. Check the seat. Then the nut. Tavin had told her that the first month, when she had stripped a bolt on a pump flange by trying to tighten it through a cracked washer. You put a wrench on a leak, you’re guessing. Clean the surface. Check the seat before you touch the nut. The leak’s always in the seat, and the seat’s always under the nut. She had thought it was the kind of thing he said about everything. She thought now that he had said it about this.
“Collar off, or pipe off?” Sera said. She was crouching beside Mara now, looking at the schematic in the notebook and at the valve.
“The collar,” Mara said. “The seat’s under it. The seat’s what’s cracked. If we take the pipe off, we’ll lose everything that’s left in it. If we take the collar off slowly, we can look at the seat.”
She looked up at the ceiling grille.
“Orison.”
“Yes.”
“The collar on this valve has been over-tightened,” Mara said. “Past its safe range. Someone tried to stop the leak by tightening it. The leak isn’t at the collar. It’s in the seat underneath. The seat’s cracked. The extra pressure from the collar is making the crack worse.”
The grille was silent for a while.
“I believe I would have noticed that,” Orison said slowly. Then, after a pause, quieter: “I did not.”
“It’s hard to notice,” Mara said. “It looks like a loose collar. It sounds like one, almost. Anyone would have tightened it.”
“You did not.”
“I almost did,” Mara said. “I heard the pipe change. That’s all.”
Orison said nothing to that.
They worked on it together. Sera took the valve key, the one from the Tern, and fitted it to the valve’s wheel on top, not to turn but to hold, so that the stem would not move when they worked on the collar. Mara laid her bare hand flat on the pipe below the collar, on the frost, which burned her palm at once with a cold so deep it felt like heat, and held it there. She needed to feel what the pipe did.
“Quarter turn,” she said. “Loosen. I’ll do it. You hold the stem.”
“Holding.”
Mara put the wrench on the collar again and eased it, the other way this time, against the threads. It wanted to stay where it was. She leaned, gently, more, and felt it give: a small grinding shift, and the collar turned back a quarter of a turn.
The pipe’s note under her palm came up, only partway, but up, out of the hollow, toward something rounder.
The hiss changed too. It went from a thin steady sound to a breathier one, uneven.
“It’s breathing,” Sera said.
“It’s letting go.”
Under Mara’s palm the crust of frost cracked. A long crack, running down the pipe from the collar, through the white ridges, with a small sharp sound like ice on a pond. The crust split and lifted at its edges, and Mara pressed her thumb into the crack, and beneath it the metal of the joint was bare, and wet, and cold, and for the first time since they had come into the chamber, it took a breath of air.