Billy’s little face lit up and my heart twisted with pain. Why shouldn’t he cry? He was only eight years old.

‘You should have …’ The sentence dries up on my tongue. I want to tell Mark that he should have talked to Billy about it, that he should have got to the bottom of whatever it was that upset him so much he felt the need to deface the photo album, but I can’t bring myself to say the words. It’ll just rub salt in the wound. It won’t make him feel any better about it. If anything, it will make him feel worse. And it won’t bring Billy back.

I slump back against the sofa, suddenly exhausted.

‘Are you sure?’ I say. ‘Are you absolutely sure that nothing happened to make Billy do that to your photos? An argument you haven’t told me about? A fight? A grounding I don’t know about? Something you took from him?’

He frowns down at his hands, then turns his head to look at me. He blinks slowly, several times, and his frown deepens. ‘What are you accusing me of, Claire?’

I don’t know. Mark has never raised his hand to Billy; he’s never hit either of the boys. He’s lost his temper countless times but he’s never done more than shout at them.

‘You think I’m behind his disappearance, don’t you?’ he says. ‘You meant what you said the other day.’

When I received the phone call from the school to say that Billy hadn’t been in I assumed he’d skived off with some mates, something he’d done several times in the preceding few months. When he didn’t return home that night I still didn’t panic. He was sulking after the argument he’d had with Mark the night before, I told myself. He was hiding out at a friend’s house, nursing hurt feelings and dented pride. But when he still wasn’t home by half eleven I began to worry.

I went up to his room and looked through his things. His schoolbag was missing. His mobile phone too. I rang him several times but each time my call went straight through to answerphone. I tried texting him but there was no answer. I had the numbers for the mums of several of his old primary-school friends so I rang them and asked if their sons had seen Billy but none of them had.

When Kira got back from college and Jake returned from work, horribly hungover after a session in the pub the day before, Mark asked if either of them had heard from Billy. They both said they hadn’t. Jake said we were over-reacting.