I stared at the drunken cop’s face and for the first time I wondered if he was insane.

‘Listen, I’m going to go now,’ I said, ‘I have to pick up my son. I can walk home from here.’

Stoner pressed a button and the central locking clicked shut.

‘That woman is my wife,’ DCI Stoner said. He stared thoughtfully at the family in the park. ‘He’s a big guy, isn’t he? Fit. Works out. Free weights, all of that. Naturally strong. But I took him.’ DCI Stoner stared at me. ‘I went to his place of work and I gave him a good hiding because of what he was doing with my wife behind my back. He dropped the charges but the bitch still had a restraining order put on me. Did you know they could do that? They can get a restraining order put on you even if you’re not convicted of anything. Where’s the justice in that? Just for sending a few hundred text messages! And you know why I beat him?’

‘Because you can do what you like,’ I said wearily. ‘Because you’re a cop.’

DCI Stoner shook his head. ‘That’s the irony, Christian! I’m a cop – but so is he! That’s the funny thing! That’s how my wife knew him. We all worked at the same station. I was a detective, he was a uniform, and she was on the clerical staff. No, the reason I beat him even though he is twice my size is because it mattered far more to me than it did to him. To him, she was just some bored married woman he was knocking off.’

‘Their relationship looks like far more than that.’

His face clouded with annoyance.

‘Whatever it became later, once she got her claws into him, at the start my wife was just a bit on the side. Believe me. And to me – well, my wife was my sun and my moon and my stars. And that bastard took it all away.’

I looked at the two mixed-race little girls on the roundabout.

‘She doesn’t look like your wife,’ I said quietly. ‘She looks like his wife.’

DCI Stoner’s mouth tightened. ‘Are you trying to provoke me? My ex-wife.’

‘Ah.’

‘Because I want to show you – I understand. I understand the way that James Caine made you feel. I felt the same way. If you didn’t want to kill him, you would be different from every other man on the planet. You wouldn’t be human. That guy and your wife – the mother of your child – they did what they did while you were putting your little boy to bed. Then he came to your home. Then you confronted him in the street. And then, when it was all too much to take, you went to his hotel to sort him out. That’s true, isn’t it?’

‘I have to pick up my son.’

The children would soon be coming out of school. I imagined Marlon’s face scanning the grown-up faces at the gates, and failing to see me, and his smile fading to concern.