When? I want to ask. I can guess the answer: after the art fair, after he moved in with me. He searched my house, looking for evidence that Mary and I were in league against him.

‘He looked Gemma and Stephen up on the internet and found what he expected to find,’ Mary tells Waterhouse. ‘Their attack on Ruth, all that. But the name Gemma Crowther kept coming up in another context too—on Quaker websites. That’s how he found out which meeting she went to. He started going too. He wanted to find out if she was the same Gemma Crowther who’d nearly killed his girlfriend.’

‘Told you all this at gunpoint, did he?’

‘He didn’t have to say anything he didn’t want to. Neither do I. I’m telling you because I want to, no other reason.’ Mary’s voice is full of scorn.

‘Did he find out, then?’ Waterhouse asks. ‘That she was the same Gemma Crowther?’

‘Not at first. Not until she mentioned that she used to live near Lincoln. Then he knew. He asked her why she moved to London. That was the test: to see if she’d changed. If she had, he said, she’d have told him the truth: what she’d done to Ruth, and that she was sorry, that she was a different person now. At the very least she’d have mentioned having been in prison, even if she didn’t say what for. But she didn’t. She lied—made up some story about wanting a change of scene and career. He knew she was a fake when she told him that.’ Mary laughs. ‘She was a healer, did you know that? What a fucking hypocrite! No loss to the world, that’s for sure.’

‘Why did Aidan give Gemma Crowther your painting?’ Waterhouse asks.

Silence. Or else they’re talking but I can’t hear them any more. When I hear Mary’s voice, I’m relieved. ‘He said they deserved each other. Gemma and the picture.’ She’s crying. ‘As if a painting’s a moral agent, as if it can deserve anything. Monday night was going to be the last time he saw her—he told me. He wanted nothing more to do with her, or me. He was going to leave Abberton with her because it seemed appropriate, he said. And then he’d be rid of us both for ever, me and her.’

‘Makes sense,’ says Waterhouse. ‘That’s why you made him lock Abberton in the boot of his car before forcing him at gunpoint to drive here. It wasn’t only about framing him for Gemma’s murder, was it? It was symbolic. You wanted to show him he couldn’t shake you off so easily.’

He’s right, isn’t he Mary? You wanted the police to find something of Aidan’s and something of yours together: his car, your painting.