“There is one thing, Chris,” I tell my client as I visit him in his little cell while he waits for his trial. He nods for me to continue. “Assuming there is sufficient evidence to have you acquitted of murder and kidnapping, there will still be a charge brought against you by the state. You need to understand that, OK?”

“What charge?”

“Probably perverting the course of justice. But it could be aiding and abetting. You did know about the murder, and helped Megan to cover it up.”

“So, what’s your plan?” he asks me. I know he wants to ask what kind of penalties he might face as opposed to murder, but he can’t bring himself to contemplate the idea that he might serve any time at all.

“Find a compelling reason why you didn’t report Megan back in February. Or find better proof that doesn’t simultaneously show you knew there was a body in that freezer.”

His eyes are a piercing shade of blue in the bright overhead light. “Just do whatever you have to,” he says in the end.

Derek is with my firm on work experience. I think he belongs to the sister of one of the partners, but I wasn’t really paying too much attention. Anyway, he is very tall, weighs about as much as my ex-wife’s miniature pinscher and apparently has a perfect memory.

I put him to work looking through every photograph taken at the Hardcastle house, those from Leah’s house, and the social media accounts of the two twins and their extended families.

“Find me something that suggests a crossover,” I instruct him. I don’t hear from him again for two days. I assume he goes home in the evenings, otherwise I think the partner’s sister would make a fuss. I also assume he goes out to get himself a sandwich or brings a packed lunch or something, but whenever I peer through the window into the darkened office he’s stationed in he is there, and he is laser-focused.

Jemima is in my office, sitting on the corner of my desk in a way that gives me the merest glimpse of her lacy underwear, when Derek knocks on the door. Jemima immediately crosses her legs and her panties are lost from sight. She raises an eyebrow at me. “Rain Man’s here,” she stage-whispers as she hops off my desk.

“I found something, sir.” Derek is holding a small stack of papers close to his chest.

I stand up and beckon him over. He’s sweating gently; there’s a sheen across his forehead. He stumbles a little as he approaches. Jemima stifles a giggle behind her hand. I will write her up for it later. You can’t take the mickey out of people in the office, it’s just not professional.

“Talk me through it,” I instruct as I take the stack from him.

He clears his throat, licks his lips, then clears his throat once more. None of it helps; his voice is reedy when he starts. “See that picture?” he says, pointing to a photo that he’s laid on the desk. He clears his throat a final time, which seems to do the trick. “It’s from Leah’s bathroom in Belsize Park.” I nod and motion for him to continue. “See that, there in the corner by the toilet? It’s a brand-new package of toilet roll. Doesn’t seem like anything at all.” He is warming up and there’s something almost endearing to his earnestness now it’s being channeled into something I want.