The Registry occupied nine floors of a tower the colour of wet sand, and every one of them smelled, to the people who could smell, like paper trying to be honest.

Nadia could tell only that it was cold. She signed in at the front desk as Nell Owens, and a clerk with a lanyard and a lip stud handed her a visitor badge on a cord. The badge said NELL OWENS - WITNESS - ESCORT REQUIRED. Her escort, when he came down, was in the same charcoal suit as yesterday, or its twin, with a paper cup of coffee in each hand.

"I did not know how you took it," said Kaveh.

"Black."

"I thought so." He handed her the left cup. "You have the look of a woman who distrusts additives."

"That's very good."

"It's the first thing you've said that I haven't had to decode." He turned for the lifts. "Fourth floor. We will pass the open-plan area. Please do not look at anyone, and do not touch anything, particularly the biscuits."

"What's wrong with the biscuits?"

"They belong to Odalys in Compliance. She keeps a ledger."

His office was a glass box with a view of the canyon wall and a desk so tidy it looked staged. A single plant. A framed certificate. A photograph, angled slightly away from visitors, of Kaveh and a tall, laughing woman in a pale coat at some Rim function, her hand on his chest, her head thrown back. Liesel Ostergaard-Banda. Nadia saw the picture and looked at the plant.

He shut the door. The blinds came down at the touch of a switch.

"Tell me," he said.

She told him, and this time she told him all of it. She hadn't planned to. She had walked up from the Floor with a story she'd built on the funicular, a careful architecture of half-truths designed to buy her a week. But he sat with his untouched coffee and his hands flat on the blotter, listening the way he had in the lift, a full-bodied, unhurried attention that made lying feel like talking to a wall. By the time she reached her father he had stopped writing.

"One bond," he said.

"One. For a Rim family. Three years ago, six weeks before he died. A young woman delivered the money. Tall, pale linen coat, a flat gold ring on her thumb. Old family. No name."

Kaveh didn't move. Not a muscle. It was somehow worse than if he had.

"A ring," he said.

"Yes."

"Plain gold. Very thin. Worn on the right thumb."

"I wasn't told which thumb." She watched him. "You know it."

"It's an Ostergaard heirloom. There are three. One belongs to Liesel's mother, Margit. One to Liesel. One to her sister Odile, who is not often in the city." He said the names carefully, like someone laying cutlery on a very hard table. "Any of them might have gone to a clinic on the Floor. Any of them might have been told to. I am saying that the evidence is not the evidence. I am not saying that I do not know what it looks like."

"Kaveh."

It was the first time she'd used his name, and they both noticed.

"I don't think she knew," he said, to the window. "I would know. I would have known. We were..." He stopped, as if the word had cracked in his hand. "We were considered a very good match."

"By who?"

"By everyone. By the Assayer. By my mother." The shadow of a thing that was nearly a smile crossed his face and fled. "My mother wept at the first verification. Mrs. Dastgheib does not weep. She stood in the Assay room in a blue dress and cried into a handkerchief the size of a tablecloth, and she told me that I was lucky, that most people spend their whole lives and never smell it. I thought it was the happiest day I would ever have."

Nadia put her cup down.

She was a person who knew exactly how many ways there were to be sorry, and had a number of them in stock, and none of them would do. So she did what she did when she couldn't be kind: she asked a question.

"How long have you been taking it?"

He turned. "Taking what?"

"Braid. The second dose. A forged bond doesn't last. I've told you the compound has two stages. The base is set by the first dose, and then the note has to be raised ninety minutes before the test, or it fades. It holds six weeks, tops. I've never made it last longer, and I'm better at this than anybody alive." She leaned forward. "Your bond has passed three annual renewals. If the note's been forged every time, someone has been feeding you the second dose in the ninety minutes before each Assay."

"I have never taken any such thing."

"Did you know you'd taken it?"

"I..." He stopped. He sat back. His hand went flat on the desk and she watched, with some alarm, the colour leave his knuckles. "I eat what I'm given on renewal mornings," he said slowly. "It's a tradition. A small ceremony. Liesel makes the tea. She makes it herself, from a tin of her grandmother's leaf, the first morning after the... she says it brings luck. She's done it every year. Three years. She's always so careful to get it right."

The office hummed. Somewhere outside the blinds, someone laughed at a joke about spreadsheets.

"That," said Nadia, "is how I would do it."

"That is how a person who loved me would do it," Kaveh said, hard and level. "To keep a thing that had gone wrong from showing."

"Or how a person who didn't."

"Yes."

"Which do you think it was?"

He looked at her, and for a moment she caught what he must have looked like at nineteen, at twenty-five, a boy who had believed every rule was a hand held out. Then it went, and the auditor returned, shutting the door in his own face.

"I do not know," he said. "I would like to find out before I am wrong in public."

The door opened without a knock.

A tall man came in, mid-forties, in a suit of pewter-grey wool, with a gentle bald head and the warm, rueful face of a family doctor. He carried a tablet under one arm. He smiled at Kaveh with real affection, and then at Nadia with a polite blank pleasantness, and she felt his eyes go over her and find, under the lanyard and the borrowed name, nothing at all.

"I'm sorry," he said, "I should have knocked. Kaveh, I wondered if you'd had a chance to look at the Glassrow file."

"Director," said Kaveh, rising. "Dov. This is Ms. Owens. She's helping with a witness statement."

"Of course." Dov Albrecht-Nwosu offered his hand. His grip was dry and warm. "Terrible business, the Glassrow affair. We've lost a very fine Assayer. I mean to see it closed properly." He held her hand a moment longer than necessary. "You're not wearing scent, Ms. Owens. How refreshing. This building is a fog of lavender. I find it hard to think."

"It's an allergy," said Nadia.

"Of course it is." He let go. "Kaveh, don't forget Saturday. The Founders' dinner. Liesel will be there? I'd so like to see you both settled on the same table." He smiled again, and left, and the door clicked shut like a very quiet exhalation.

Kaveh was still standing.

"The Director of the Assay Office," Nadia said. "The man Wren Castellanos-Boyd wrote to."

"Yes."

"He was in your doorway for ninety seconds, and he asked about the file, and about Saturday, and about whether Liesel would be there. And he's the one person in this building who didn't ask me one single question."

"Noted," Kaveh said, and for the first time since she had met him it did not sound like a joke.

"There's something else," she said. "The Floor is paying fifty thousand for the Chandler's name. Cash, by Friday. Strangers have been stopping my courier at traffic lights."

"Paying who?"

"Whoever sells me. It's on the back boards of Chirrup."

"Then it isn't the Registry. We do not pay for names; we subpoena them." He pressed two fingers to the bridge of his nose. "That leaves someone who wants you found and does not want it written down."

"Could be your Director."

"Could be a great many people." He crossed to the window and stood with his back to her, the wet-sand light on his shoulders. "My renewal falls in nine days. If Liesel makes the tea, and I drink it, I pass. If I do not drink it, I fail, in front of the Assayer, and the Registry begins an inquiry into one of its own. Which is what I should want. Which is my duty."

"But?"

"But I would be failing in front of someone who is probably watching for it." He turned. "I think I need a different kind of tea."

Nadia stared at him.

"You're asking me to make you a forged bond dose."

"I am asking you to keep a lie alive for nine days so that I can find out who is telling it." The words came out stiff as starch, and he heard it, and winced. "I am aware of how that sounds from a man with my job."

"It sounds like fraud."

"It is fraud. I will be committing it." He went to the desk, picked up his coffee at last, and drank all of it, like a man swallowing a sentence. "In exchange, you will have my protection while you stay out of the way of the Director, and you will have the resources of an office that can find out who is bidding for you. I will do my best not to arrest you before it is over."

"Your best."

"My very best."

"That's the least reassuring thing anybody's said to me all week," said Nadia. She reached across the desk and took his hand, shook it once, hard, surprised by the heat in it. "Fine. Nine days. But I'm not making it in a corporate bathroom. I'll do it at my lab, with my gear, and you'll come down to the Floor to take it like a normal customer."

"A customer."

"With a punch card," said Nadia. "Every tenth is free."

The corner of his mouth moved. It wasn't quite a smile, but it was at least a lease on one.

On his desk, beside the coffee, the little photograph of Liesel's laughing face turned slightly in the draught from the closing door.