‘Idle curiosity – it’s what the app’s about. There’s a competitive element.’

‘And a nosy element.’ She smiles like we’re in this together.

‘Well, yes. It’s supposed to be fun.’

‘Until your partner stops to talk to the woman you suspect him of having an affair with.’

‘I did not suspect them. I didn’t think they’d even met.’ My palms have started to sweat. I wipe them surreptitiously on my jeans.

‘Your kids go to the same school. You share a friendship group. Are you asking us to believe that Nick and Anna never ran into each other?’

‘She only moved round here in January. And it’s not as if we socialized together. We probably would have done eventually, but these things take time.’

‘You were jealous of Anna, weren’t you? When you started to suspect that Nick was involved with her. How did that make you feel?’

I frown. Why is she pushing this so hard? ‘It didn’t make me feel anything, because I am not jealous of her.’

That isn’t entirely true. I remember how I felt on seeing Anna’s and Nick’s footsteps stop climbing; the sharp ache under my ribcage, the feeling of nausea and the surge of adrenaline.

‘Did you follow Nick that night? It would have been understandable in the circumstances. You were already suspicious about his relationship with Anna. He made yet another excuse to go out on his own. Weren’t you curious to see where he went the second time?’

‘None of that even occurred to me.’

‘When you went looking for him, did you walk or go by car?’

‘I walked.’

‘Where did you go?’

‘Around the local area.’

‘Did you go straight home?’

‘Yes, I did.’

‘You didn’t take a detour down Camomile Avenue, out of curiosity?’

‘No.’ A little worm wriggles in my tummy. I’ve told a lie.

‘I’m surmising,’ Grant says. ‘If it crossed your mind that he might be with Anna Foreman, the obvious thing would have been to have a look at her house.’

‘But it didn’t cross my mind,’ I insist. ‘I trusted him.’

‘Are you sure about that? You tracked Nick on the app.’

‘I didn’t track him,’ I say impatiently. ‘As I’ve explained, In-Step tells you how many steps your friends are doing. There’s no map; it’s just numbers.’

‘Fine, but you were curious about where he’d been and upset enough about your suspicions to mention them when you reported him missing. It would have been natural for you to wait and see if he came out.’

I sigh. ‘But I didn’t. I went home, and I went to bed. I finally fell asleep about an hour later. When I woke, he hadn’t come home.’

Grant leans back, and Marsh lifts his gaze from the files.