Kaveh Dastgheib's flat was on the eleventh floor of a building called Tallow Court, and it looked like a hotel room that had given up on guests.

White walls. A grey sofa with the cushions squared. A kitchen where the only objects on the counter were a kettle and a ceramic dish containing one lemon. In the living room, a single bookcase held the Registry's Operating Protocol in eleven volumes, a dictionary, and a row of crossword compilations whose spines had been labelled with the year. On the wall above the sofa hung one print: the canyon at dawn, in a frame so plain it seemed apologetic.

"It's very clean," said Nadia, from the doorway.

"I am told it is a little austere." He put his keys in a bowl. "Liesel wished to redecorate. I said I would consider it. For three years."

"What stopped you?"

"I did not know what I would want."

It was half past three in the morning. They had left Saoirse's flat in a clatter of coats and rain, Sol driving the sleeping doctor home to Imelda's bakery loft, Liesel and Saoirse taking a taxi up to the Rim to confront Margit before breakfast. Kaveh had said very little in the lift. He had said less in the corridor. Now he took off his tie, folded it, and set it beside the lemon, and she understood that he had brought her here for the same reason he did everything: because it was the logical place to be.

"There is a spare room," he said. "It is used for storing ironing. I can clear it."

"I'll take the sofa."

"I wouldn't dream of it."

"Kaveh. You've been awake for twenty-two hours and your hands are shaking. I'm going to sit up and read this thing again, and you're going to lie down on that sofa, and if you argue, I'll make you eat the lemon."

His mouth moved. Not a smile, but its architectural drawing. "Noted," he said, and lay down on the sofa in his shirt and trousers, one forearm over his eyes, and within four minutes he was asleep.

She had not known he could. She stood for a time and looked at him: a man of thirty-three, long and straight even in sleep, lines at the corners of his eyes she hadn't noticed in daylight. He looked younger and more tired. He looked like someone who had been carrying a full tray for a very long time and had finally been allowed to put it down.

She found the throw on the back of the armchair and laid it over him, carefully, the way you cover a sleeping child.

Then she took the laptop to the kitchen table, opened Wren's spreadsheet, and did what she had avoided doing in the lab with everyone watching. She looked at what was not on the first sheet.

There was a second tab. It was labelled, in the same dry hand, *notes*.

It was short, and it was not a spreadsheet. It was a diary, of a sort: a column of dates and a paragraph beside each, written with the clipped precision of a woman used to filing things she did not want to be found. Nadia read it by the light of the extractor fan, with a cup of Kaveh's very good tea going cold at her elbow.

*14 Feb. Approached again by D. Tells me again I am valuable. He says it gently. He always says it gently.*

*3 Mar. #4 (E.) bonded to Councillor Hartigan-Lam, registered. No dose. Held at first Assay. Held at second. D. very pleased.*

*19 Mar. #6 (M.) bonded to Chair of the Rim Planning Committee. No dose. Held. I asked D. how. He said "It is a talent."*

*2 Apr. I do not believe it is a talent.*

*17 Apr. Looked up the original Braid research. Pablo Q.'s paper, 2011, withdrawn. Abstract: "the third note is not a product of two scents but of a catalytic absence." Did not understand. Understand now.*

*18 Apr. We do not smell of nothing. We smell of a space. A scent-shaped gap. A wolf standing beside us has nothing to push against, so his own note reflects back on itself. Two wolves cannot braid because each is only himself. A wolf and one of us can braid with ANY partner, because the gap holds the partner's shape. We are the third note.*

*20 Apr. It is not that we cannot be read. It is that we are the thing that reads back.*

*22 Apr. D. is not calibrating Tether. D. is arranging marriages.*

Nadia put down her cup.

The refrigerator hummed. Somewhere below, eleven floors down, a night bus hissed and pulled away.

*Every placed scentless is now bonded to someone with a Council vote. Hartigan-Lam. The Planning Chair. A judge. Seven of the eight are placed, or have been approached for placement. Every bond holds without a dose. D. is not building a machine. He is building a bloc.*

*24 Apr. If he wants a bonded scentless in every chamber, he does not need Tether. He needs Tether for cover. He needs the Assay to be unforgeable so that no one will ever test the bonds he has already made.*

*26 Apr. I am going to tell the Director's office what I know. I have written to him. I will not tell Odalys; she would worry.*

There was a final line, dated three weeks ago, the week before Wren died.

*I think I am number nine. I think he already knows what I found out.*

Nadia sat very still.

She thought about the lift at Marrow House: *it was as if someone wrote it.* She thought about Pablo's page, *we are the third note*, written in a hand that did not shake. She thought about what it was to be a gap in a room full of people who needed edges, and how, for twenty-nine years, she had felt that as a deficiency. A defect. A mistake in the weave.

*We are the thing that reads back.*

When she looked up it was getting light. The window over the sink had gone from black to bruised grey, and the first tram of the morning was crawling up the funicular like a ladybird. She had been reading for three hours.

"You have found something," said Kaveh.

He was sitting up on the sofa, hair on end, the throw around his waist. He was looking at her the way he had looked at the Assay swab in the lift, with a care that wasn't suspicion but its opposite.

"Yes," she said. "I think I know why Dov wants the scentless. And I think I know what your Director would like most in the world."

"Tell me."

"Me," said Nadia, "in a registered bond with a senior Registry auditor. With no dose."

Kaveh was quite still.

"The idea Liesel had," she said. "The one that solves everything. Dov would love it. He'd be thrilled. He'd put a ribbon on it." She turned the laptop to face him. "If you and I bond, we'd pass the Assay on the first try, every time, with no dose, because that's what we do. Forever. And you'd be the Registry's best nose with a scentless mate, and he'd own us both."

He read it all. He read it slowly, the way he read everything, and she watched him get to *arranging marriages* and stop, and go back to the beginning.

When he had finished, he said, "Then we do not do it."

"That's what I thought."

"We dissolve Liesel's bond on Friday. By mutual consent, as she proposed. There is no need to establish another." He took a breath. "I will protect you in the ordinary way. By being very difficult to remove."

She hadn't known she'd been braced for something else until the relief arrived.

"That's the correct answer," she said.

"I know. I find it unsatisfying." He rubbed his eyes with the heel of his hand. "Nadia. Before we leave this table, I wish to say one thing, and I wish to say it clearly, so that it cannot later be misunderstood. Whatever I decide to do about my life, I will not do it because a document tells me it is logical. If I ever ask you to stand beside me, it will be because I want you to. Not because it is useful. Not because it is safe."

The kettle ticked as it cooled. Outside, the whole canyon was catching light, one terrace at a time.

"I'll hold you to that," Nadia said.

"I'd like to say something kind," said Kaveh, getting up and going to the kitchen, "and I find I do not have the equipment. May I make you breakfast instead?"

"What have you got?"

He opened the fridge and regarded it for a long, grave moment. It contained a carton of eggs, a block of butter, and a jar of something labelled in Liesel's looping hand, *Mum's quince*.

"Eggs," he said. "And toast, if the bread is not a rumour."

"You cook?"

"I have an excellent eggs." He cracked one into a bowl with a single clean movement. "My father could not be relied upon for meals. I learned four things. This is one of them."

"What are the other three?"

"How to read a lease. How to lose gracefully. And how to tell when a person is lying to you by the way they ask for the salt." He did not turn round. "You, for the record, have never once asked for the salt."

She sat at the table in the grey light and watched him whisk, with the unnecessary precision of a man dismantling a bomb, and thought that if there was a rule about not noticing someone's forearms before six in the morning, she had been breaking it for a week.

The eggs were, annoyingly, excellent.

They were halfway through the second slice of toast, in a silence that for once was not an armed one, when his phone rang. A number she did not know. He listened for a few seconds, and she watched his face go through an astonishing series of changes, and then settle on something between grief and fury.

"Understood," said Kaveh. "We are on our way."

He put the phone down.

"That was Odile," he said. "Her safe was opened in the night. Volume ten is gone. And Liesel is not at the Rim." He swallowed. "She has not been seen since she arrived."