The photograph of Box One was still on her phone. That was the first thing Dilly checked, standing in the Fairhold stairwell with the fire door shut and her pulse going in her ears, and it was there, forty-second in a camera roll of 3,118 pictures, between a blurry shot of a vault lock and a screenshot of a pie meme someone had sent her in a cruel mood. She had taken it on Wednesday night, 11:41 p.m. She had shown it to Sel. She had not sent it to anyone.

She opened the settings and went through them in the methodical order she once used to sweep a hotel suite. Location services. Installed apps. Sharing. Backups.

There it was: a cloud service with a green leaf for an icon, enabled four years ago, the kind of thing you tick yes to when the phone nags you at two in the morning. Its name was KARI-SHARE, which she recognised after a moment with a feeling like missing a stair. She had not seen it in years. It said LAST SYNC: THURSDAY 12:04 A.M. And under it, in small grey letters: SHARED WITH 2 PEOPLE.

She stood very still.

She knew who had set it up. He had been eighteen, and she had been twenty-five and sleeping in a hotel in a different state every second week, and her mother had been frightened by the thought that Dilly's photographs of her childhood might disappear in a lost phone. So Rustam, who was good with computers in the way that boys are good with computers when they are not good with anything else, had made a family account for the whole Karimov household. Photos, documents, her father's old voicemails. He had picked the password. She remembered because he had said it aloud, laughing, over the phone from the laundromat. Password one-two-three, chat, no, kidding, it's way better than that.

She had left Sel in the board room with Margit and the door locked, and a promise of forty minutes. She went down the six floors by the back stairs, past the cleaning cupboard, past the night porter's table, out through the service door into the alley, and called him.

He picked up on the fourth ring. "Hey, hi, I'm live, can I call—"

"Turn it off."

"Dilly—"

"Rustam. Turn it off. Come to the roof. Now."

He came in eleven minutes, wearing a hoodie with the sleeves pushed up and his phone in his fist like a stone. She was waiting where the iron ladder met the tar, with her own phone in her hand and the screen facing him. He saw it as he came over the parapet. She watched his face go through three expressions in order: curiosity, recognition, and a dismay so total that it looked almost like peace.

"Oh no," he said.

"What is the password?"

"It's, um."

"Say it aloud."

"It's the same one I use for, like, everything." He swallowed. "It's not bad. It's got a number. And a capital. And a symbol, an exclamation mark, you know?" He looked at her face. "It's the name of my first channel. And the year I started. And the mark."

"Your first channel is public."

"It's got eleven followers, Dilly, it's been dead for years—"

"It's the name on your profile. It's in your bio. Anyone who wanted to try it would try it in under a minute." She heard herself, hard and cold and entirely unfair, and could not seem to stop. "I took a photo in the vault. It went to the cloud. It went to your account. And on Monday morning a man I'd never met said the words Box One to my husband."

"Your fiancé."

"Rustam!"

He flinched. Everything in his body flinched, and it went through her like a wire.

"I didn't know," he said. His voice had gone up into the register it only reached when he was frightened, the child's register, thin and cracking. "I swear on Dad. I didn't know it was synced. I thought I turned that off. I turned it off for my own phone, that's the only one I checked. You never said you were using it. You've got like four hundred pictures of Ona's tomatoes on there, I didn't think there was anything—" He stopped. He pressed the heel of his hand against his eye. "I was going to be so good this week. I wasn't going to say anything. I was going to be the one thing about this you didn't have to worry about, and I made it worse."

She had her mouth open for the next sentence. It stayed open. The sentence was a good one. It was about responsibility and carelessness and the cost of a single weak thing in a chain, and she had delivered it, or its cousins, to a hundred junior agents over the years. It would have made her feel better.

She closed her mouth.

"Sit down," she said instead.

He sat on a crate. After a moment she sat beside him. The geraniums in their tins shook slightly in the wind off the river, and a pigeon walked along the parapet with the air of a creature who has seen everything.

"I'm sorry I shouted," she said.

"You didn't shout."

"I was loud inside."

"Yeah." A watery laugh. "I could hear it."

"You did a stupid, normal thing that everybody does. It isn't a crime. It's just that I need you not to do a stupid, normal thing for about a year." She turned her phone over in her hands. "You're going to change every password you own tonight. We'll do it together. I'll check each one. A different one for each, a manager, an authenticator, the lot. Then you're going to show me the login history for this account."

"There's a login history?"

"There's always a login history. It's the only honest thing in the machine."

He nodded. Then he did not move. He sat with his elbows on his knees and looked at the river, and she realised he was working up to something, the way he used to work up to telling their mother about a broken window.

"Can I say a thing?"

"Yes."

"I know I'm the loose bit. I know that. You've got Ona's shop and Sel and the whole town and I'm the one who talks to his phone like it's a person." He gave a small crooked grin that did not reach his eyes. "But I'm not stupid, Dil. I'm good at one thing. Finding stuff out. That's all the channel is. Somebody posts a clip, I find out where it came from. Somebody says a thing, I find out who said it first. It's the only reason I have any followers. I could help. Not by posting. By looking."

"It's dangerous."

"It's a login history."

"Behind the login history there's a man who walked into a vault with a dead woman's card."

"Then I'll be careful and he'll be dangerous and we'll both be doing our jobs." He bumped her shoulder with his. "Dad would've said yes."

It was a low blow, and he knew it, and she let it land. Their father had been a surveyor in Tashkent before he had been a laundry-van driver in Corliss Ferry, a man who measured the world in small exact angles and trusted anyone who could tell him how far away a thing was. He had taught her to count steps. He had taught Rustam to take apart a radio. She had spent fourteen years thinking of that as her inheritance and her brother's as a hobby.

"Fine," she said. "You look. You don't post. You don't tell the chat. You tell me, and only me, and you do it from the shop's machine, not your own."

"The chat doesn't know anything about it."

"Rustam."

"I'm just saying, they'd love it. Forty-one people, maybe more now. They keep asking when the wedding is." He caught her expression. "I won't say! I'm joking! I'm one hundred percent joking. Mostly. Okay, ninety percent."

She almost laughed. It surprised her how close it was to the surface.

It took twenty minutes with the laundromat's old laptop on an upturned crate and Rustam's fingers flying. When he had killed the sessions and reset everything, the account's activity page unfolded on the screen like a map of a crime.

Most of it was theirs. Rustam's phone, in the flat above the shop. Dilly's phone, from the Thornquist house. Their mother's old tablet, which had once, for six unexplained minutes, logged in from a bus in Phoenix. And then, at the bottom, in the plain grey type of a system that does not editorialise, a single entry that did not belong.

NEW DEVICE. THURSDAY, 12:09 A.M. IP: 10.40.7.22. LOCATION: CORLISS FERRY (PRIVATE NETWORK). DEVICE: FDRT-TAB-07.

"What's ten-forty?" Rustam said. "That's a weird address."

"It's not an address." Dilly was already on her feet, with the unpleasant, familiar cold in the pit of her stomach. "It's a block. It's the internal range of a company with a very large private network. And FDRT is Fairhold." She read the line again. 12:09. Five minutes after she had left the vault.

Thursday morning. She had been in the building at midnight. Sel, Margit, Pascual, herself. And one more person she had not known about.

She called Junie.

"Hey, wait, I'm literally in the middle of a mood board—"

"Junie. Fairhold issues tablets. Who has FDRT-TAB-07?"

"Oh, uh, give me a sec." A clatter of keys. "It's in the asset register. Executive suite, floor six. Office of the Chief Operating Officer. Hester's."

"Who is Hester?"

"Hester Nwosu-Kallio. COO. She runs, like, everything that's not Sel. Thirty years at the bank. Beloved. She brought me soup when I got my wisdom teeth out." A pause. "Why?"

"No reason." Dilly stood looking out at the river. "Where was she on Wednesday night?"

"Home, I think? Why would she be in? Oh, wait, she was in touch about the funeral flowers. She said she was home and it was killing her not to be at the vault, because she's always asked to be there for the Close and Mrs. Odessa never let her. She said it was a family thing." Junie's voice had slowed. "Dilly, why?"

"Because someone used her tablet to log into my brother's account, at 12:09 on Thursday morning, on the Fairhold network. And I was standing in the same building."

There was a silence on the line, a long, thick one, and in it she could hear the rustle of a girl who had been told not to say anything and was trying very hard to obey.

"Dilly," said Junie, in a tiny voice. "Hester's the one who has the master key to the sideboard drawer. The ninth key. The one Sel forgot."