This made no sense. Alex had told me he wanted to split Sam’s time, do their best to keep things normal for him. Anna’s crazy, he said, she won’t let me go, she’s jealous. That had chimed with my experience of her shouting at me in the street.

‘Did she tell you why she shouted at me – what had annoyed her so much?’

‘Oh. Well, because she – well, she knew who you were, and she didn’t like it.’

I stared at him. ‘What? She knew I was Casey?’ No one had known. How the hell could Anna have found out, of all people?

‘She thought so. She’d been shown this picture of you – Casey Adams – and thought maybe it was you. I thought it was kind of crazy, to be honest, but she insisted, and she told Alex, though he didn’t believe her of course. Said she was just jealous.’

‘She told Alex?’ Alex had already known I was Casey? He hadn’t said anything when I went round to his flat to tell him everything.

‘Yeah, but he didn’t believe her. Neither did I. But she was right, I guess.’

My mind was crumbling, every bit of information sending me in different directions. I looked at my watch – I’d been out too long, and it was getting dark already. I was here alone by a lake with a man I had never met before. Would I ever learn?

‘Ciaran, listen, I think you should talk to the police. The main detective. DS Hegarty. He’s nice, he wants to figure this out. They haven’t charged me yet, despite all the evidence. They probably know she was seeing someone. They’re smart. I just . . .’ I took a deep breath, looking into the dark depths of the lake. Imagined it closing over my head, carrying me away, the shock of the cold, of surrender. ‘I have to sort this out. I can’t go back there.’

‘Where?’

‘Prison.’

‘Oh yes.’ He looked uncomfortable.

‘Rule yourself out, at least. Tell him Anna had Sam on the night she was murdered.’

Meaning, if it was true, that Alex had no alibi. Where had he been, if not in his flat looking after Sam?

Ciaran was nodding. ‘It’s just scary. My wife . . .’

‘Well, believe me, I know all about that. But they’ll find out in the end, and you’ll just look guilty.’ We were back at the head of the path now, and I could see cars going past and the odd pedestrian. I was safe. ‘Thank you for contacting me. It was brave.’

He nodded. ‘I just – she deserves justice, is all. And I don’t think either of us has been told the full story.’

‘Ciaran – how did she feel about Alex?’

He paused a moment. ‘Honestly? I think she was afraid of him. She never said, but just – little things.’

‘All right. Thank you. Take care.’