‘Where’s the painting she gave you?’ Waterhouse asks me. ‘Can we see it?’

Pressure builds in my head. ‘I haven’t got it any more.’

‘How come?’

‘I . . .’ I look at Aidan, but he turns away, lines up two more lengths of glued moulding. Why should I lie to protect him when he won’t tell me what I’m protecting him from? ‘I gave the picture to Aidan,’ I tell Waterhouse. ‘I haven’t seen it since.’

Aidan shoves the underpinner away. ‘Mary Trelease is dead,’ he says through gritted teeth. ‘Dead people don’t paint pictures. Ruth brought home a picture by somebody—it was ugly, so I took it to a charity shop.’ He’s lying.

Charlie Zailer takes a step forward. ‘The front bedroom at 15 Megson Crescent is full of Mary’s paintings. So full I could hardly get in. You say you didn’t know she was an artist. Weren’t the paintings there when you were, when you killed her?’

‘He didn’t kill her!’

I’m surprised when he answers. ‘No. No paintings, nowhere in the house.’

I catch the look that passes between Sergeant Zailer and DC Waterhouse. They’re about to give up.

‘I have to go out,’ Aidan says.

‘Where?’ I ask, at the same time as DC Waterhouse is saying, ‘Do you believe in ghosts, Aidan?’

‘No. I believe in the material world: facts and science. I don’t believe dead women come back to life,’ he says quietly.

‘Then, in your opinion, who is the woman that Sergeant Zailer, DC Gibbs and I have all met at 15 Megson Crescent? If you’re certain you killed Mary Trelease, then the woman who looks like her and owns her home and paints her paintings, who has her passport, driving licence and other documents—she must be a ghost, surely—a very well-equipped one at that.’

‘I told you: I don’t believe in ghosts.’ Aidan walks over to the small basin in the corner and turns both taps on hard. The workshop’s plumbing is ancient; there’s as much noise as there is water. ‘The next time you come looking for me, be ready to charge me, or I’ll have nothing to say.’ He washes and dries his hands.

‘You didn’t answer Ruth’s question,’ says Waterhouse. ‘You volunteer that you killed someone years ago, but you won’t tell her where you’re going this afternoon.’

‘Get out.’

‘I think we’ve overstayed our welcome, Simon,’ says Charlie Zailer.

‘You did that when you crossed the threshold,’ Aidan tells her. She gives him a contemptuous look on her way out.

Waterhouse lingers. ‘You came to us, remember? Or does your memory wipe out things that have happened as well as inventing things that haven’t?’

He’s gone. They’re both gone. Aidan slams the door, leans his head against it. Once he’s breathing steadily again, he says, ‘You said you went to the police. You didn’t tell me you went to Charlotte Zailer.’

I haven’t got the energy to pretend it was a coincidence that she turned up. Let him think what he wants.