Even the familiar sensation of wind streaming past his ears couldn’t obliterate his guilt. He’d achieved nothing for Freya. He’d added to Steph’s worry. And, on top of everything else, why had he lost his temper with Yvette? There had been a time when he’d considered her his only real friend. He knew it was in her job description, but she’d been the one person who’d actually seemed to get it. What it was like to be undercover, what it could cause you to do.

She’d cried as Paul had told her about Freya’s disappearance. But, when it came down to it, he’d only been interested in whether she knew where Sanderson was. His emotions had got the better of him when she’d claimed Glover told her very little about cases or targets, past or present, only as much as she needed to counsel the undercovers. He had been particularly cagey about the Sanderson operation, she’d added, and though Paul knew that was true, he’d still stormed away from her, reverting to anger and mistrust. The old paranoia had him in its clutches again: Who was on his side? Who was real?

Do you think there’s any chance Sanderson still lives in Nottingham? he’d pressed her. Still on the same estate, even?

Yvette had eyed him with concern. You’re not thinking of going there?

Paul hadn’t answered. He’d long ago promised himself he’d never go back.

As he ran past the boats and paddling swans that were the landscape of his current life, he couldn’t help seeing the Chainwell Estate superimposed over it. Graffitied playgrounds, boarded-up pubs, vandalized bus stops. And the tower block that had been Paul’s parallel universe for three years. His mind’s eye dived through an upper-floor window, disturbing a flurry of memories. Mostly everyday domestic scenes, but always with something slightly amiss, a glance or a silence or an atmosphere.

Sanderson’s oppressive presence. The sorrow that had weighed in the air.

Nathalie silhouetted in the kitchen window, biting her shredded nails.

Nathalie, Nathalie, Nathalie. If he allowed himself to think of her, it was usually in fragments: green eyes, thin wrists, dark hair on a white pillow. But lately the dots had begun to join up, the gaps to infill . . .

It’s been pulled down, Yvette had told him: The one piece of information she’d had. The tower block. It was deemed unsafe. Nottingham City Council demolished it a few years ago.

Paul had been ambushed by emotions, hearing that. Relief that he wouldn’t have to go inside it ever again; exasperation at another dead end; a swell of unhappiness he didn’t want to make sense of. He’d tried to destroy that place in his memory, and now he couldn’t fight the idea that he’d somehow made it happen for real.