‘We were worried that he might not keep quiet after the police started searching the park,’ she said in the same matter-of-fact tone. ‘But it turns out that prostitutes are more easily bribed than most, and young Jules was no exception. Not really a surprise, is it?’

‘All right,’ I said. ‘You win.’

Beth shifted her grip on the shotgun slightly, but kept it trained on me.

‘I could tell you were getting close this morning, that the penny was finally going to drop. I just knew it. So I had to get you here one more time, and I knew you’d do the full white knight routine for Alice if you thought young Mr Kolnik had turned up.’

‘So what happens now?’

‘The finale,’ Beth replied. ‘Mel – you know what to do.’

From a pocket Mel produced a pair of surgical gloves and proceeded to put them on, the tight rubber snapping into place. From her handbag she took a black-handled kitchen knife, a length of clothes line, duct tape, black leather gloves and a black balaclava. I recognised it. All of it. The winter gloves I’d got last Christmas, the balaclava from a pre-William skiing holiday. The tape and clothes line had been in the bottom of my toolbox for years.

‘What are you doing?’ I said to my wife, a hollow feeling in the pit of my stomach.

Mel didn’t answer me. The knife in her hand, she drew up Beth’s sleeve to expose the skin. Hesitated.

‘Do it,’ Beth urged her. ‘Go on.’

Mel ran the blade down Beth’s forearm, not hard enough to break the skin.

‘I can’t,’ she said quietly.

‘Yes you can. Harder.’

Mel tried again and this time Beth pushed her arm against the blade. A bright line of blood appeared as the knife cut a groove in her forearm.

‘That’s more like it,’ she said, blood starting to flow freely from the wound.

‘Doesn’t it hurt?’ Mel said, her voice shaking.

‘It’s fine. Carry on with what you’re doing.’

Mel dropped the duct tape and the clothes line on the floor by the bed, and the bloody knife on the floor about six feet from me. Maybe I could dive for the knife before Beth shot me.

I inched my feet wider apart on the floor.

Beth said: ‘A terrible thing happened here today, Joe. You broke into my house.’

‘I came to protect you, I thought you were in danger.’

‘Sweet. What actually happened was that you broke in downstairs, carrying that knife.’

She indicated the black-handled boning knife on the floor. It looked familiar, and I realised why: it was from our kitchen at home. I used it to cut up lemons for Mel’s G & T.