‘I gave it to Aidan to prove to him that he couldn’t have killed you,’ I try to explain. ‘He kept insisting he had, no matter what I said. Abberton had your name on it, and the date: 2007. He told me he’d killed you years ago.’

‘How did you know I’d signed and dated it?’ Mary turns on me. ‘I hadn’t when I brought it in to Saul’s place last June.’

I tell her, as coherently as I can, about the Access 2 Art fair.

‘My God,’ Mary mutters, chewing her lip until drops of blood appear. When she next takes a drag of her cigarette, it comes away red at the end, as if she’s wearing lipstick.

‘I gave Aidan the picture and never saw it again,’ I tell her. ‘He wouldn’t tell me what he’d done with it. Mary, I’m sorry . . .’

‘A present’s a present,’ she says in a brittle voice. ‘I gave it to you, you gave it to him, he gave it to her.’

‘What did you do? When you saw it, I mean?’

‘What could I do? I got in my car and drove home. When I left, Gemma Crowther was alive and she was with Aidan Seed. That should tell you everything you need to know about your boyfriend.’

‘Why did the police talk to you?’ Why not me? Maybe they’d tried. I ignored everyone who came to the workshop yesterday; maybe one of those knocks was the police.

‘Some nosey bastard neighbour saw me and came and asked who I was—I should have lied but I didn’t think quickly enough. As it turned out, it was lucky she saw me. She watched me leave, and heard the two gunshots after I’d gone. Waterhouse had gone, I’d gone—the only person still there with Gemma was Aidan. Even the cops should be able to work it out.’

Something hard and huge is welling up inside me. Why do I feel as if I’ve let Mary down? It’s crazy. I owe her no loyalty. Aidan’s the person I love and ought to trust. He’s never intentionally hurt me, and she has.

It hits me then: I’ve forgiven her. If I can forgive Mary, then I can forgive Aidan, whatever he’s done. And after that? Where would I stop?

‘Ruth? What’s the matter?’

‘I’m the one,’ I tell her.

‘What do you mean?’