‘Not much. She just said that you know Kate and you’re concerned about her behaviour.’

‘Kate slept with my husband. And now he’s dead.’

Mona stops walking again. ‘Oh. That’s…I’m so sorry.’

‘She was the last person to see him,’ Harper continues. ‘But she’s not admitting to anyone – including me – that she even knew him. Nobody knows except for me. And now Faye Held.’

‘And how exactly do you know she slept with him?’

Harper lets out a deep breath. ‘I know how this sounds, but I had a camera in the flat. Jamie and I had a property we rented out and we were between tenants. I…let’s just say I had suspicions that he was using it to take women back there.’ Harper takes out her phone and scrolls to the picture of Jamie and Kate. ‘Here’s the proof.’

Mona stares at the photo. ‘Kate’s changed a lot. I wouldn’t have recognised her. Her hair’s completely different. Darker than I remember.’

‘I think it’s common for people to alter their appearance if they’re trying to start over and forget the past. Run from something.’ Harper puts her phone back in her pocket.

‘Makes sense I suppose. But sleeping with someone doesn’t make you a murderer, does it?’ Mona says.

They continue walking. ‘But if you’ve killed someone before…’

‘Graham White. Hearing that name…it makes me…well, in a way, it was my fault. Kate shouldn’t have been walking home that day. She should have been hanging out with us by the canal. Then it would never have happened.

‘You can’t think like that,’ Harper says. She doesn’t know all the details, but she needs to keep Mona talking. ‘You arenotresponsible for what happened to Graham White. And I’m not responsible for what happened to Jamie.’

Mona pauses, dabs her eyes. ‘But I’m the one who set off the whole chain of events. Kate and I had had an argument, and I keep thinking what if we hadn’t? Even now I think like that. It’s stayed with me all these years. Then maybe he never would have crossed paths with Kate. She points to a bench on the other side of the trees. ‘Let’s sit over there. I think I’m ready to share this story.’

‘Kate and I fell out that day. Badly,’ Mona says, once they’ve reached the bench. ‘It was over this boy – Kian. It seems so trivial now, but back then it was colossal. We were only fifteen.’

‘Friends and boys are everything when you’re that age,’ Harper says, remembering the huge crush she’d had at that age on Craig Summers. She never did have the courage to speak to him, and the two of them only ever eyed each other from a distance. Kids’ stuff. But huge at the time.

‘We both liked Kian,’ Mona says. ‘But we never talked about it, and I felt bad because even though I’d liked him first, Kate was always talking about him so I could never explain how I felt. But she knew. Once when she was at my house, she found an old diary I’d written in. It had everything in there – all my feelings about Kian. About my whole life. I caught her reading it but she never said anything. Just shut it and slipped it back under my bed. Kate was strange like that. A closed book. She refused to talk about what I’d just seen her doing. And what can you do if someone refuses to speak?’

That fits with everything Harper has witnessed from Kate. ‘So what happened on the day Graham White was killed?’

‘We were all hanging out by the canal. We’d broken up from school early as it was the last day of the summer term. Anyway, I was kind of seeing one of Kian’s friends – Robbie. Kian always seemed to have a girlfriend so I’d given up waiting for him. Anyway, Kate needed the toilet and there weren’t any nearby so she went into town. She was gone for ages. And in that time, I’d broken up with Robbie and admitted to him I had feelings for Kian. He was a real arse about it – shouting out to everyone that I wanted Kian. Calling me a slut. Humiliating me in front of the other boys. It was horrible. But then, Kian came to my defence and told Robbie to back off. They had a fight, then Kian and I were left alone. We were just talking and I admitted it was true that I liked him. That’s when he kissed me and…it probably went too far, and I didn’t think Kate would see us. I thought she’d decided to go home. She’d been gone for so long.’ She stares at Harper. ‘Please don’t judge me – I’d liked him for so long. You know that feeling when someone is under your skin and you just can’t shake them?’

Harper understands. Jamie was under her skin the second she met him. And he still is. But her deep-seated love for Jamie turned into something else. And even now he’s dead, Jamie underlies all her actions. ‘I get it,’ she says.

Mona folds her arms across her chest. ‘I don’t like talking about this. I’ve blocked it out all these years.’

Harper nods. ‘I understand. But I need justice for my husband. Please, Mona. Help me make sure Kate Mason pays for what she did.’

Mona hangs her head. ‘Kian and I were…you know…together. In the woods. And suddenly Kate was there screaming and shouting. She ran over to me and grabbed me by my hair, dragging me away from Kian. She told me Kian was her boyfriend and I’d betrayed her. But they weren’t together, I swear. She was just infatuated with him. She was grabbing me, throwing punches, and I was terrified. She’d always had a bit of a temper but I’d never seen her that bad before. Kian dragged her off me and told her to calm down, but it was like she didn’t even hear him. She ran off, and I remember how her face looked – so red with rage. She screamed that I’d pay for this as she was running off.’

‘Did you tell the police all of this?’

‘No. They never asked, and I just wanted to forget it happened. Robbie was already spreading it around that I was some kind of whore and I’d slept with Kian. I had to keep my distance from all of them when we went back to school. I just shut myself off and then my mum moved us to St Albans.’

‘I know this is hard, but it’s been a long time…You could go to the police now if it helps me to prove Kate killed Jamie.’

‘Just because Kate and I had a fight and she basically attacked me – it doesn’t prove anything about what happened with Graham White.’ Mona shakes her head. ‘I’ve already told Faye that I won’t speak about this publicly to anyone, and that includes the police. I’ve got my job and the church to think about. I can’t get dragged into that awful mess.’

But there is another way. ‘What about Kian?’ Harper says. ‘He could testify to Kate’s behaviour that day.’

Mona’s defiant expression falls. ‘That might be a bit difficult.’

‘Why?’

‘Kian died a few years after it all happened. He got really drunk at a party and ended up walking in front of a car. Funny, though – Kian never seemed the type who’d drink excessively. It always seemed like he was just drinking for the sake of it. To look cool or something.’