The lift took ninety seconds to reach them. Mira counted the descent the way she counted a titration, one drop at a time, waiting for the color to turn.
She took her hand off Gideon's before it arrived. Not because she wanted to. Because a woman holding a man's hand in front of whoever stepped out of that door would be read, and she could not afford to be read. She peeled her fingers away one at a time and folded them at her side, and she watched him notice her do it, and she watched him decide not to say anything, and the deciding was somehow louder than a word would have been.
The resealed precursor sat behind its glass in the middle of the vault, dull now, a gray pearl where minutes ago there had been a live and hungry light. The silver pattern that had climbed her wrist during the signing had gone quiet, sunk under the skin like frost melting into a pane. Her own record and his were one file now. She could feel the fact of it the way you feel a tooth pulled, the absence more present than the thing had ever been.
The lift opened.
Dr. Oren Fane stepped out alone, in the soft gray coat the licensed floors gave their pioneers, carrying a slim case she recognized before she recognized him. He had trained her on that case. He had taught her to open it in a particular order so that nothing inside touched air in the wrong sequence. Seeing it in his hand was like seeing her own younger fingers held up in evidence.
"Mira," he said. Gentle. He had always begun gently. "You've been very busy."
"Director Armit sent you," Gideon said. Not a question. He had positioned himself a half step forward of her, angled toward the lift, and he had done it without any theater, the way another man would shift his weight. Mira noted it and filed it and could not entirely stop noting it.
"The Director sent a request for a status report," Fane said. "I came because I heard the vault sing. There is a frequency the Root Witness makes when its scaffold is engaged. I have waited eleven years to hear it. I did not expect to hear it stop." He set the case down on the floor, unhurried, and looked at the gray pearl behind the glass. Something moved in his face. Not grief. Closer to the way a man looks at a proof he cannot reconstruct. "Tell me what you did."
"We resealed it," Mira said. "The membrane's inert. The tower's safe. You can write that on your report and take your case back upstairs."
"You resealed it," Fane repeated, and now he crouched, elbows on his knees, at the level of the glass. He studied the pearl for a long moment. His pauses had always been a kind of instrument. They made you want to fill them, and filling them was how he learned everything he knew. She kept her mouth shut. She had learned that much from him too. "With what," he said finally, "did you reseal it, Mira? The Root Witness scaffold cannot be closed by containment. It can only be signed shut by its source. And you would never sign yourself into a vault. You have spent your whole life making sure nothing could be traced back to your hand." He turned his head. He looked at Gideon. "So."
Gideon said nothing.
"So," Fane said again, softly, and stood. "You put an investigator's hand on it. A man who shares her credential. Clever. Genuinely clever. The scaffold accepted him as an extension of the source, and it closed." He almost smiled. "You improvised a solution I would have taken three months and a review board to authorize."
"Then we're done," Mira said.
"No." The word was so kind it took a second to cut. Fane picked his case back up. "You've misunderstood what the scaffold is for. It was never only a lock. It was the reference. The one uncontaminated instance of the tandem chemistry, held pristine, so that when I performed the separation I would have something to calibrate against. You separate two fused signatures by measuring both against the original and pulling them apart along the seam. The seam is written in that pearl." He nodded at the glass. "Was written. You signed it shut. You bound the reference into a closed record with your own two joined hands inside it. There is no longer a clean instance to calibrate against. There is only the copy, and the copy is you."
The vault was very quiet. Mira heard the filtration cycle somewhere behind the wall, the tower breathing.
"Say it plainly," she said. Her voice came out level. She was proud of that, distantly, the way you are proud of a reading you took while your hands were burning.
"The separation cannot be performed," Fane said. "Not by me. Not by anyone. The procedure requires the scaffold, and the scaffold is spent. Whatever you are now—" his eyes moved between them, once, "—you will remain. There is no precursor left in the tower that can undo it. I would have to grow a new source witness from a living original, and the only living original—" he inclined his head at her, courteous, terrible, "—is standing in a closed archive with her signature already inside the file."
She had wanted one thing for two years. Separate the marker. Get her hands back to being her own hands, tradeable to no one, legible to no machine. Every calculation she had run since the ampoule broke had ended at that door, and Fane had just walked in and welded it shut and thanked her for the initiative.
She did not look at Gideon. That was the discipline it cost her. She kept her eyes on the pearl and she did not look at the man who had pressed his hand to the glass over her protest, who had made this exact loss with the exact intention of sparing her the worse one, and she thought, with a clarity that felt like cold water, that if she looked at him now her face would do something she could not take back in front of Oren Fane.
So she was looking at the pearl when Gideon spoke.
"How long have you known," he said, "that resealing it would end the separation?"
Fane's pause this time was a beat too long.
"The question is whether you knew," Gideon went on, and his voice had gone flat and narrow, the register Mira had learned meant he had stopped asking and started measuring. "You said you waited eleven years to hear the scaffold sing. You didn't come down here for a status report. You came down here hoping it would be engaged, because an engaged scaffold is a scaffold you can extract before it closes. You wanted the reference in your case before either of us understood what it was worth." He took a step. Not toward Fane. Between Fane and the glass. "You're not here to help her separate. You're here because the only clean instance of the science you built your name on was about to stop existing, and you would rather have it in that case than in her."
Mira looked at him then. She couldn't not.
He wasn't looking at her. He was standing square in front of the resealed precursor with his marked hand open at his side, putting his own body between her mentor and the last thing her mentor wanted, and he had reasoned his way there out loud, from a pause and a coat and a case, the way he reasoned his way through a false raid order or a locked door, and she understood that this was the thing about him she was not going to be able to put down. Not the signing. Anyone desperate enough will sign a glass. This. That he watched, and counted, and named the exact shape of a man's want a full second before the man knew he'd shown it.
Fane held very still. Then he set the case down again, and this time he opened his empty hands, and he smiled the gentle smile, and it was, for the first time in Mira's memory of him, a fraction too late.
"You'd have made a fine chemist," he told Gideon.
"I'm a fine investigator," Gideon said. "Answer the question."
"I knew," Fane said, "that the reseal would consume the reference. Yes." He looked at Mira. All the paternal warmth was still there, and under it, for anyone who'd been trained by him to see it, the calculation running its quiet arithmetic. "I hoped to reach you before you finished. I did not reach you in time. That is the truth, Mira, and you may believe as much of it as your training permits."
"None of it," she said.
"That's the girl I taught." He picked the case up. "But you should want me now more than you have ever wanted anything, because I am the only person alive who understands the seam between you two well enough to guess whether it can be reopened by any means at all. And I have not decided yet whether it can."
The lift stood open behind him, waiting.
"There is one route left," Fane said. "It is not elegant. It would require a second living original. A source witness who is not you." His pause returned, long and soft and precisely aimed. "You have always insisted you developed the tandem chemistry alone. If that is true, then no such person exists, and you and the investigator are one file until the archive burns." He stepped back into the lift. "If it is not true—if there was ever another hand in that early work—then somewhere in this tower is a person whose skin can still be grown into a reference. I would think hard, Mira, about which lie is more expensive."
The doors began to close.
Mira did not move. Beside her Gideon had gone still in the particular way that meant he had heard the crack in her breathing and was waiting to see whether she would seal it herself.
She already knew the name. She had spent two years making certain no one else ever would.