The Fairhold Building on Merchant Street had been designed to make people feel small and then relieved.

It was seven storeys of pale river stone with a revolving door like a held breath, and by day it was full of ordinary things: tellers, a children's savings corner with a plastic bear, a queue for the Tally help desk. By night it was a different animal. At ten past eleven, when Pascual brought the car into the service alley and Dilly got out first and counted four doors, three cameras and a fire escape that did not go where its sign said it did, the building had the hushed, over-lit emptiness of a hospital ward after visiting hours.

"It was my grandmother's rule," Sel said, getting out slowly. "She thought a bank that put its sleep first would be out of business by Easter. She said a bank has to be awake for the people who can't be."

"That's very noble."

"She also said it would stop me taking up golf."

He was better tonight. The pills, the three hours' sleep she had forced on him with the bedroom door open and Pascual in the corridor, had put a little brown back in his face. But the walk from the car to the service door still cost him. She watched his weight drift to his left foot at the second step and shift back again, as if the right were an uncertain friend. She said nothing. She had learned that morning that if she said anything he would make a joke, and that the jokes got longer the worse it was.

Margit was waiting at the door with a key card on a lanyard and a clipboard she did not need. "You are four minutes early," she said. "Good. I dislike late. Late is a kind of lying."

"Is that on the wall somewhere?" said Dilly.

"It is on a card in my desk. Come."

They went down in a service lift that smelled of floor polish. The vault level was two floors under the street, and the corridor outside it was lit a soft amber, and at the end stood the door. Dilly had expected something from a film. It was a pale grey slab as tall as a man and about as thick as a mattress, with a modern keypad and a wheel from another century, and the whole assembly had been so polished by hands that it shone like a coin.

Beyond it was a small round room with a desk in the middle.

That was all. There was an old oak desk with a green leather top worn pale at the edges, a lamp with a brass arm, an inkwell that held no ink, and a chair with arms. On the desk lay a single large ledger bound in black cloth, open to a page that was already ruled and dated. Along the walls ran rows of deposit boxes, steel doors with little numbered locks, like a very dull set of drawers in a dead man's house. Under the desk was a small floor lamp that threw a pool of gold on the carpet. The room felt like a place where people spoke in low voices, whether or not they meant to.

"The Close is done by hand," Margit said, "because Mrs. Odessa believed that a thing a person must write is a thing a person must think about. The system reconciles every account in the city from ten o'clock. At eleven fifty-five it produces a summary. I read the summary aloud. The Keeper reviews the totals, which are printed here, and signs the ledger at eleven fifty-eight. I countersign. The signature is photographed at the desk and released to Tally. That is the whole of the ceremony."

"No audience?"

"The audience is the city. It does not need to be in the room." Margit's mouth moved a fraction. "Mr. Thornquist-Adeleke. Please sit."

Sel sat. It was an awful thing to watch, though she could not have said why. He took the chair as a man takes a pew in a church he no longer believes in. He laid his left hand on the leather. He laid his right beside it, and Dilly saw it was already trembling, and that he was pressing the heel of it into the desk to still it, and that this was a nightly performance, a small private struggle between a man and his body that he had been fighting since he was twenty-two.

She stood by the door. The old bodyguard's reflex: back to a wall, eyes on the exits, the corner of the room in her peripheral vision. She counted. One door. One camera in the ceiling. One man who might be dying and one woman holding a pen.

"Eleven fifty-five," said Margit, and began to read. "Total deposits, four hundred and eleven million, six hundred and four thousand, three hundred and twelve dollars and nine cents. Total outstanding loans, three hundred and ninety-eight million, seven hundred thousand—"

She read for two and a half minutes in a clear, dry, unhurried voice that made the numbers sound like weather. Sel listened with his eyes half closed. A little pulse beat steadily in his throat. At eleven fifty-seven and forty seconds he opened them, and picked up the pen. It was a plain steel nib, fine, old. Dilly saw his fingers shake once and then, by an act of will she could feel from across the room, still.

At eleven fifty-eight and no seconds, he signed.

A. Thornquist-Adeleke. A loop, a straight line, a slight forward lean. It took four seconds. Margit countersigned beneath it in the same ink, and reached for the small stamp on the desk, and pressed it onto the page with a soft click. A blue-black crescent stood on the paper like a small bruise.

Overhead, in the amber light, something in the ceiling blinked once. Dilly pulled out her phone, and watched the icon on the Tally screen, the little blue hand, turn green. Closed. Sleep well, Corliss Ferry.

"Thank you," said Margit, to no one in particular. It sounded like grace.

And Sel put his head down on the desk.

It was not a collapse. She was across the room in two strides and she could see it was not, the breath still going in and out, the hand still moving. He simply set his forehead on the green leather for ten seconds, with his eyes closed, and let the whole of himself go slack, a man putting down a weight he would pick up again in twenty-four hours. When he lifted his head, his face wore the exact expression she had seen on the soldiers at the end of a long parade.

"That," he said, "is the worst part of my day."

"Every night," said Dilly.

"Since I was twenty-two. My father signed for twenty years and I sat in that chair, there, in the corner, on a stool, with a book." He smiled faintly at nothing. "He used to let me read the totals aloud. I was very proud. I thought that the numbers were a kind of music."

"How long did he—"

"Forty-one," Sel said gently. "He was forty-one."

She did the sum in her head and wished she hadn't. Sel was thirty-three.

Margit had moved to the side of the room, to a steel cabinet she opened with a key from her chain, and she was running her finger down a long printout. "I should show you the log," she said, without turning. "If you intend to guard this place, Ms. Karimova, you ought to have the door record. It prints every entry. There are three keypads, four card readers, and the time-lock. Each is logged."

"I'd like that," said Dilly.

Margit brought the printout to the desk and laid it down. It was a long thermal roll, the paper slightly curled, a column of dates and times and initials, and Dilly knelt on the carpet to read it, the way she had once read hotel floor plans in a stairwell at midnight. Most entries were dull: Margit, 6:48 a.m., open. Margit, 7:02 p.m., close. Cleaning staff, Tuesday, Thursday. The nightly Close at eleven fifty-eight. A steady metronome of routine, a thing like a heart.

She ran her finger back through the week. Back to the day of the death. Odessa Thornquist had died at four in the afternoon on Tuesday. The logs on Tuesday were empty after six.

She stopped.

Wednesday, 3:12 a.m.

The entry read: CARD READER 2. ACCESS GRANTED. O. THORNQUIST. DOOR OPEN 00:07:41.

The room went quiet in a new way.

"What is it?" Sel said.

She turned the roll toward him with one finger and watched him read, and watched Margit, who stood behind him, read it over his shoulder. Margit's lips parted, the first unguarded thing Dilly had seen on her face.

"That is not possible," said the Vault Clerk.

"Whose card is reader two?" said Dilly.

"Mrs. Odessa's. It is the founder's card. It has not left her person in eleven years. It is—" She stopped. "It was in her handbag. Her handbag was in the bedroom. I was told it was sealed with the effects, on Tuesday evening, with the rest of her jewellery, by Bettina."

"She died at four," Dilly said slowly. "This is eleven hours after. Seven minutes forty-one in an open vault, at three in the morning, with no cameras?"

"There is one camera," said Margit. "It records to a drive. It was serviced on Monday. There is no footage from Wednesday morning at all."

Sel's fingers moved on the ledger, very lightly, as if smoothing a page. "Someone," he said, in his careful, fraying voice, "walked into my grandmother's vault while her body was still warm in the house, using her card, and walked out again, and I sat in this chair afterward, and signed, and noticed nothing."

"Not without noticing," said Dilly. She stood and brushed the carpet from her knees. She looked at the rows of deposit boxes, steel doors with their little numbered locks, hundreds of them, each one holding someone's will or ring or secret. "We noticed just now. Which means whoever it was has been waiting for us to."

"Why?"

"I don't know." She took out her phone and held it up, and photographed every box on the east wall, and every lock, until she found the one that was not like the others. It was Box 1, at eye level, in the centre of the wall, and the little brass plate beside its keyhole was clean and bright and unscratched. It had not been touched in years. And the dust on its upper edge, in the lamp's amber light, had a long curved wipe through it, the width of a palm.