‘What do you mean?’ She turned to him, fiddling with the lead round her neck.

‘I tried to do what you’re doing, three years ago. My parents told me to leave it alone, that I was only going to make things harder for myself, but I just couldn’t accept it.’

‘You tried to investigate?’

He gave her a mock salute then, barking, ‘Yes, Sergeant.’ Like he couldn’t let himself be vulnerable, couldn’t let himself be serious long enough to expose a chink in his armour.

‘But I didn’t get anywhere,’ he carried on. ‘I couldn’t. I called Naomi Ward when she was at university, but she just cried and said she couldn’t talk about it with me. Max Hastings and Jake Lawrence never replied to my messages. I tried contacting Andie’s best friends, but they hung up as soon as I said who I was. Murderer’s brother isn’t the best intro. And, of course, Andie’s family were out of the question. I was too close to the case, I knew it. I looked too much like my brother, too much like the “murderer”. And I didn’t have the excuse of a school project to fall back on.’

‘I’m sorry,’ Pip said, wordless and embarrassed by the unfairness of it.

‘Don’t be.’ He nudged her. ‘It’s good to not be alone in this, for once. Go on, I want to hear your theories.’ He picked up Barney’s stick, now foamy with dribble, and threw it into the trees.

Pip hesitated.

‘Go on.’ He smiled into his eyes, one eyebrow cocked. Was he testing her?

‘OK, I have four working theories,’ she said, the first time she’d actually given voice to them. ‘Obviously the path of least resistance is the accepted narrative of what happened: that Sal killed her and his guilt or fear of being caught led him to take his own life. The police would argue that the only reasons there are gaps in the case are because Andie’s body hasn’t been recovered and Sal isn’t alive to tell us how it happened. But my first theory,’ she said, holding up one finger, making sure it wasn’t the swear-y one, ‘is that a third party killed Andie Bell, but Sal was somehow involved or implicated, such as an accessory after the fact. Again his guilt leads him to suicide and the evidence found on him implicates him as the perpetrator, even though he isn’t the one who killed her. The actual killer is still at large.’

‘Yeah, I thought of that too. I still don’t like it. Next?’

‘Theory number two,’ she said, ‘a third party killed Andie, and Sal had no involvement or awareness at all. His suicide days later wasn’t motivated by a murderer’s guilt, but maybe a multitude of factors, including the stress of his girlfriend’s disappearance. The evidence found on him – the blood and the phone – have an entirely innocent explanation and are unrelated to her murder.’

Ravi nodded thoughtfully. ‘I still don’t think Sal would do that, but OK. Theory three?’

‘Theory three.’ Pip swallowed, her throat feeling dry and sticky. ‘Andie is murdered by a third party on the Friday. The killer knows that Sal, as Andie’s boyfriend, would make for the perfect suspect. Especially as Sal seems to have no alibi for over two hours that night. The killer murders Sal and makes it look like a suicide. They plant the blood and the phone on his body to make him look guilty. It works just as they planned it.’

Ravi stopped walking for a moment. ‘You think it’s possible that Sal was actually murdered?’

She knew, looking into his sharpened eyes, that this was the answer he’d been looking for.

‘I think it’s a theoretical possibility,’ Pip nodded. ‘Theory four is the most far-fetched of the lot.’ She took a large breath and did it in one. ‘No one killed Andie Bell, because she isn’t dead. She faked her disappearance and then lured Sal out into the woods, murdered him and dressed it up as a suicide. She planted her own phone and blood on him so that everyone believed she was dead. Why would she do this? Maybe she needed to disappear for some reason. Maybe she feared for life and needed to make it look like she was already dead. Maybe she had an accomplice.’

They were quiet again, while Pip caught her breath and Ravi ticked over her answers, his upper lip puffed out in concentration.

They had come to the end of their circuit round the woods; the bright sun-stroked road was visible through the trees ahead. She called Barney over and put him on the lead. They crossed the road and wandered over to Pip’s front door.

There was an awkward moment of silence and Pip wasn’t sure whether she should invite him inside or not. He seemed to be waiting for something.

‘So,’ Ravi said, scratching his head with one hand, the dog’s with the other, ‘the reason I came over is . . . I want to make a deal with you.’

‘A deal?’

‘Yeah, I want in on this,’ he said, a small tremor in his voice. ‘I never had a chance, but you actually might. You’re an outsider to the case, you have this school project excuse to open doors. People might actually talk to you. You might be my chance to find out what really happened. I’ve waited so long for a chance.’

Her face felt full and hot again, the shaking edge in his voice making something tug inside her chest. He was really trusting her to help; she’d never have thought this would happen at the start of the project. Partners with Ravi Singh.