‘He told me about the party after the school play when you two first got together.’ Another piece of evidence that I had held in my hands – and failed to see what it meant. ‘But that was when you were teenagers. How did you get from that to this?’

‘Teenagers are real,’ Mel said quietly. ‘It’s adulthood when we get lost, forget who we are.’

‘Come on, Mel, you can do better than that. This is me you’re talking to, your husband. I know who you are.’

‘You don’t get it, do you? Teenagers are honest. They’re true – that’s why they feel so vulnerable. It’s easy to forget that with all the other junk that gets in the way as you get older. Work, marriage, kids, mortgage. I woke up one morning and realised I’d turned into someone I didn’t recognise, someone I didn’t even like any more. And then Beth and I bumped into each other again at Charlotte and Gary’s wedding a couple of years ago and it all just came back, like being teenagers again.’

‘That was the party where you said you made the mistake. A drunken kiss that led to his obsession with you.’

Beth said: ‘There was a drunken kiss all right, but not with boring old Ben.’

‘That was where the two of you got back together?’

‘Like waking up again after twenty years in a coma,’ Mel said quietly.

‘This is not you, Mel. This isn’t reality.’

‘I haven’t forgotten what’s real,’ she said. ‘Who I really am.’

‘Then what about our son? What about William? What about me?’

‘You pushed us into this corner,’ Beth said. ‘If you’d kept plodding along like you’ve done for the last ten years of your life – boring old Joe, head down, stuck in your rut – you needn’t have been involved. But as it is –’

‘As it is, you’re framing me for a crime I didn’t commit.’

She jabbed the shotgun towards me.

‘That was your choice. You got involved when you didn’t have to, when you stuck your nose in. And then, almost like it was fate, you presented us with an opportunity that was too good to pass up. Gift-wrapped and tied with a bow.’

Now the shock was receding, it was starting to become clear: I needed to get out of this house, grab William and take him somewhere safe. Somewhere far away from these two.

I needed to take the initiative.

‘There’s something you should both know.’

‘What’s that?’

‘DCI Naylor agreed to meet me here,’ I lied, checking my watch. ‘He’s going to be here any minute.’

‘You called him?’

‘At King’s Cross.’

‘Not from your mobile, you didn’t. Or did you use a landline, like you did on Wednesday?’

‘What?’