‘Kat must have strangled him,’ Saskia says, her voice finally sombre. ‘Then taken a photo when he passed out. There’s a bright red line across Mark’s neck, and a snake of material next to him. One of those cheap ties maybe. You know what this means, don’t you?’ she says gently. ‘Kat is more dangerous than Mark. We need to tell the police, urgently, especially now you’re here alone. Kat clearly did this for you, to protect you, but minds like hers, they can swerve faster than Lewis Hamilton. You could be her next victim.’

Beth swipes her thumb across the screen to scroll away from the photo. She can’t bear to look at it. She knows Mark survived the attack, but not whether he’ll fully recover, or even regain consciousness. Is Beth supposed to feel guilty, responsible, for that too? And what will she say to DC Stone? That it wasn’t her husband who attempted to kill Mark, but her mentally ill dog walker? But swiping away from the photo only exposes another one of her, taken, like them all, without her knowledge. She tosses the handset onto the coffee table in disgust, then changes her mind and shoves it down the deep crevasse of the sofa.

Every muscle in Beth’s body feels taut now. She looks at Saskia on the opposite sofa, her long limbs softly draped over the cushions. Is that smugness on her face, or sympathy? Excitement or concern? ‘How did you know I was at Painshill Park today?’ she asks suddenly.

Saskia’s face twitches. ‘I didn’t.’

‘Yes, you did, you mentioned it in your message, said you hoped it was fun.’

‘Did I?’ Saskia looks away, clearly buying time, perhaps hoping that Beth will notice her discomfort and change the subject. Beth waits, and eventually Saskia surrenders. ‘Um, maybe I saw your location on Google Maps,’ she mumbles. ‘When I was, um, checking some directions for Tim.’

‘Google Maps?’ Beth has a sense of tumbling, but her body doesn’t move.

‘Yes, you shared your location with me, remember? That night out in Camden?’

Beth’s mind careers backwards. A gig in north London. Saskia arriving late. Getting swept up by the live music. ‘You track me?’ she asks, trying to keep the horror out of her voice.

‘No,’ Saskia squeaks. ‘Well, hardly ever. Only when I need to know where you are and I don’t already, which is rare, like today, with those detectives on your doorstep.’

Beth tries to breathe normally but it comes out in shudders. ‘And yesterday?’ she whispers.