The police questioned everyone after Billy was reported missing: his friends, his teachers, his relatives, even Liz and Caleb next door. I spoke to Josh, one of his friends from school, who told me what they’d asked him. ‘How long have you known Billy?’ ‘When did you last see him?’ ‘Do you have any idea where he might have gone?’ ‘What social media does Billy use?’ The police spoke to his granny and granddads, his uncle Stephen, Mr Edwards and Miss Christian at the school.

Mark.

They spent a lot of time talking to Mark, with me and on his own. They asked him to talk them through the argument the night before, word for word, and asked him question after question about Billy’s reaction and whether he thought what had happened might be enough to prompt him to run away.

A child doesn’t disappear for no reason, that’s what I kept telling myself. But there was never a reason. Not until I found the photo album. I don’t … I can’t … let myself believe that Mark would ever hurt Billy but I’d never be able to forgive myself if the truth lies between the covers of that grey album. I need to tell the police. I need to give it to them.

‘For God’s sake, Claire, say something!’

I force myself to look him in the eye. Then I tell him a bare-faced lie. ‘No, I don’t think you were responsible.’

‘Thank God.’ He sags into himself and runs his hands over his face. ‘Thank God for that.’

Neither of us says a word for several minutes, then I reach into my pocket and pull out my phone. I turn it over in my hands.

‘Mark?’

‘Hmm.’ He makes a low guttural noise from behind his hands.

‘Did you run into anyone while you were at work today?’

His fingers slip from his cheeks and he twists his face towards me. ‘What do you mean?’

‘Did you bump into anyone we know?’

He closes his eyes and rubs the thumb and forefinger of his right hand over his temples as though it hurts to think. ‘Yeah. I … I bumped into Billy’s form teacher. Um …’

‘Edie Christian.’

‘Yeah. I bumped into her outside one of the practices. Nevil Road Surgery, I think. Why?’

I place the phone on the arm of the sofa. ‘No reason, just wondered.’

‘What is it?’ He gives me a searching look.

‘Nothing.’ I glance at the photo album, propped up on the sofa between us. ‘Nothing at all.’