There isn’t a cloud in the sky, so I pull on some warm gear, stuff a box of biscuits and a flask of coffee into my old backpack and go to the hills. I have no obvious affinity to Guildford. It wasn’t where I grew up, or went to school, my university town is Brighton, my first proper boyfriend lived in Clapham along with all the other young graduates I knew. But I had decided years ago that I wanted to live in this small city, with its steep ancient high street and easy access to the trails of the North Downs. That is where I head now, knowing a few hours in the crisp sunshine of a bitter winter day will make everything clearer.

I walk for an hour, waiting for the epiphany to strike. But nothing comes except a jumble of images, real and imagined: Chris and Leah in flagrante delicto, Leah’s face staring out from the freezer, Tom clinking his whisky glass against mine. Over these images plays a soundtrack, out of time so the sound and pictures don’t line up: the thump of a wine bottle hitting bone, the plop of her phone sliding into the water, “you like that, don’t you?” said in my husband’s voice, “you’re not like I thought you’d be,” said in Tom’s.

I stop on the brow of a hill, looking down into the valley below, and drink my coffee as cold tendrils tease their way through the gaps in my scarf. With almost numb fingers I stuff everything back into my pack and set off once more, waiting for clarity. Still nothing.

How do you get away with murder? That needs to be the focus. Onwards I tramp. You need to think about the body, the voice in my head keeps saying. But no inspiration comes.

Just after eleven, Tom rings Leah’s phone.

“Hey, beautiful,” he says, his voice warm. “Having fun in deepest, darkest Sussex?”

I had told him I was going to visit a friend for the weekend. “Yep. It’s good to catch up. Remember old university times.” Fuck, fuck, fuck. Leah didn’t go to university, didn’t even do A levels. She made a big thing about it in the book and on social media. #universityoflife and all that.

“I thought you—” He cuts himself off and laughs in that gorgeous deep baritone. “Another one of your professional quirks, I presume?”

“Something like that.” It couldn’t really be so easy that he would just think Leah played a professional part, could it? But no, this only works if there is never any suspicion. From anyone. In Emma’s words, I need to be better.

“I… er…” he begins. “That is… errm… can I see you, on Monday, when you’re back?”

I know I should turn him down, switch this whole thing off and get on with making Leah disappear, but I can picture him, his hand running through his hair, the boyish hope on his face. In my head, he’s standing on a stone kitchen floor not wearing any socks, and I worry his feet must be freezing.