Unit 19

They left the penthouse at seven, in the grey hour before London made up its mind about the day.

Sebastian drove. There was a flask in the cup holder - tea, one sugar, no milk - and Imogen held it in both hands and decided not to ask when he had learned how she took it, in case the answer embarrassed one of them.

"Storage 4 opens at eight," he said. "The unit has been rented since 1999. Cash, yearly, always in November."

"Twenty-seven years of rent on a unit nobody visits."

"Somebody visited." He changed lanes without hurrying. "My grandfather kept a private ledger at the house. Unit nineteen appears in it once a year, in his own hand, next to three words: the long game."

They rode in silence for a while. The text from last night sat between them, three words on a lit screen. Stop digging. Please.

"For the record," Sebastian said, "politely is how he does it. Sorrell spent thirty years moving problems without raising his voice. The wreath at your mother's funeral. The cash for Danny's note. The please."

"You think it's him texting."

"I think warnings cost him nothing and buy him time." His hands were at ten and two, schoolboy correct. "I also think whoever wrote please knows you well enough to know you'd read it as a threat. A stranger writes stop. Someone who knows you writes please, because please is the word that keeps you up at night."

"You're wrong," Imogen said. "Please is the word that makes me dig."

"Yes," he said. "I'm counting on it."

Storage 4 sat behind a tyre depot in Leyton, a brick building wearing forty years of rain. The office smelled of instant coffee and damp cardboard. The woman behind the desk had a laminated sheet of rules and a name tag that said PAM, and she looked Sebastian up and down the way people look at an expensive car parked where expensive cars do not park.

"Unit nineteen," he said, and laid down the brass key from Walter's papers, tagged 19, and the authorization card that had been folded into the last page of Walter's letter.

Pam checked a book bound in red vinyl, and her eyebrows did a slow climb. "Walter Crowther. And - " she squinted at the card, " - Imogen Hartley. Added the week before he passed, in the same hand. That'll be you, then." She slid the visitor log across. "Sign here. Funny thing. You're the second lot this week."

Imogen felt Sebastian go still beside her, the way a dog goes still before it barks.

"Unit nineteen doesn't get visitors," Pam said. "Not in the nine years I've worked here. Then Tuesday, a gentleman, and today, you."

"Tuesday," Sebastian said. "Did he sign the log?"

"Everyone signs the log. Rule three." She tapped the laminated sheet.

Unit 19 was halfway down a corridor of padlocked doors, under a strip light that flickered like it was thinking it over. The brass key turned easily. Twenty-seven years old, and the lock had been oiled.

Imogen noticed that first. Somebody kept the lock oiled.

Inside: a single bulb, a camp chair, and brown boxes stacked with a librarian's patience, each labelled in Walter's small, arrogant hand. MERIDIAN - ACCOUNTS 1998. MERIDIAN - STAFF ROTAS. MERIDIAN - INSURANCE. And on a folding table at the back, set out as if for players who had only stepped away, a chess set.

She knew it at once. Ebony and boxwood, the white queen's crown chipped - the twin of the set in the penthouse study, the one Walter had played on alone, both sides, every Sunday of Sebastian's childhood.

"The game isn't finished," Sebastian said quietly.

The pieces stood mid-battle. White was winning. White was always winning; his grandfather had no patience for losing, even against himself. Sebastian reached to move a black knight and Imogen caught his wrist.

"Don't. It's a message."

She had played chess against debt collectors' clocks, against hospital rosters, against her brother's moods. She knew a position arranged to be read. Black's king stood boxed in by its own pawns, and the white king - she picked it up, and it was heavier than a chess piece has any right to be.

The base unscrewed.

Inside, wrapped in a square of nurse's uniform cotton so old the blue had gone grey, lay a safe-deposit key and a folded slip of paper. The key was stamped MERCANTILE TRUST - 118. The note held one line in Walter's hand:

The fire had three witnesses. One is dead. One is paid. One raised a nurse. Bring her. - W.C.

Sebastian read it twice. "My father," he said. "He never talked about the fire. Not once in thirty-four years." He turned the key over. "Mercantile Trust, Threadneedle Street. They keep boxes for a century if you pay."

"Walter paid," Imogen said. "Walter paid for everything except the part that mattered." She wrapped the key back in the cotton, slowly. "One is dead - your father or my grandfather. One is paid, and that has to be Sorrell. And one raised a nurse." She looked up. "He means my mother. But your father is dead, and my mother is dead, and if two of the three witnesses are gone, then whatever is in box one-eighteen is the only witness left that talks."

"Then we go to Threadneedle Street today."

"We go when it opens. And we tell no one. Not Danny. Not Moss. Not your lawyers." She put the white king back, gently, on its arranged square. "The leak ran through your house once."

They signed out at nine-forty. Pam took the log back, and Sebastian turned it toward himself, casual as a man checking the weather, and read the line above his own.

Tuesday, 14:05. Unit 19. A. Sorrell - in the handwriting that had signed for Walter's effects the night he died.

"He was here," Imogen said in the car park, very quietly. "Five days ago. He stood in that unit for an hour. The lock was oiled, the chair was moved, and there wasn't a fingerprint on the boxes because a man like that wears gloves. He was looking for what we just found."

"And he didn't find it." Sebastian started the engine. "He doesn't know where Walter hid it. He only knows the game is being played. Knew."

Her phone lit up in her lap.

Unknown number. Five words this time:

He knows about the box.