Did I? Doesn’t every parent? I wasn’t blind to Billy’s faults. I knew there was a reason he was acting up at school and getting into trouble for graffitiing. Something was making him unhappy but I didn’t know what because he wouldn’t let me in. He could have told me what he’d seen outside the pub that night but he kept it to himself. Did he do that to protect me? Or did he think I thought Mark was perfect? There’s a twisted irony there that I can’t deal with right now.

‘How could you do it?’ I say. ‘How could you carry on living in our house? You saw how upset we were. How could you watch that, knowing what you did? We were searching for our son, we were desperate and all along you knew … you knew where Billy was.’

‘I didn’t know he was dead.’ She glances away.

‘I don’t believe you.’

‘I didn’t. I swear. I heard him hit the side of the train when he tripped, but when I got up I couldn’t see him. He wasn’t by the tracks. And I got scared. I ran back to the van. I thought he’d come after me.’

‘You can’t have been that scared. You went back to our house and got into bed with Jake.’

She shakes her head. ‘Not straight away. I sat up in the kitchen. Granddad was dead. I couldn’t go to Mum’s. And I told myself … I convinced myself … that there was another way out. I decided that if Billy came back … when Billy came back … I’d tell him that I’d keep having sex with him. I’d have told him anything to stop him from telling Jake what we’d done. I love Jake. I love him so much.’

‘Maybe you should have thought about that before you slept with his brother.’

‘I know.’ She closes her eyes tightly.

‘Kira, you went back to our house! You sat in our kitchen like nothing was wrong when Billy was lying in the undergrowth dying. You could have rung an ambulance. You could have saved him!’

‘I was scared. I thought he’d hurt me.’

‘Hurt you?’

‘You don’t know what he did, Claire.’ Her eyes glisten with tears. ‘The things he’d seen on the Internet … the things he made me do—’

‘No.’ I hold up a hand. ‘You could have stopped that, Kira. You had a choice.’

‘Did I?’ She looks at me, her eyes lifeless.

‘You must have realized that Billy was dead when you woke up the next morning and he hadn’t come back.’