I walk towards the pile of bin-bags that look so out of place on the elaborately patterned rug. I pull open the one nearest to me, taking care not to rustle the plastic any more than I have to. Apart from a pair of small pink Wellington boots on top, it’s full of women’s clothes. Geraldine’s: lots of black trousers-velvet, suede, corduroy, no jeans-and cashmere jumpers in all colours. Did she collect cashmere? I look in another bag and find dozens of bottles, tubes and sprays, and about twenty paperback books, mostly with pastel-coloured covers-peach, lemon yellow, mint green. Beneath these there is something with a hard edge, something that swings into my ankle as I move the plastic sack, making me grunt through clenched teeth.

I look over my shoulder to check I’m safe, then reach to the bottom of the bag and pull out two chunky wooden frames. Photographs of Geraldine and Lucy. Quickly, I hold them at a distance, not ready for the shock of seeing them so close to me. Geraldine is smiling, standing with her head tilted to one side. She’s wearing a white scoop-neck T-shirt, a black gypsy skirt, silver sandals with straps round the ankles and black sunglasses on her head like a head-band. She’s got the arms of a silver-grey sweater tied round her waist. There’s a cherry blossom tree behind her and a squat, flat-topped building, painted blue, with white blinds at the windows. She’s leaning against a red brick wall.

I bring the picture closer, staring, feeling my heartbeat in my ears. My arms are shaking. I know that place, that stubby blue building. I’ve seen it. I’m pretty sure I’ve stood where Geraldine is standing in this photograph, but I can’t remember when. The last thing I wanted to discover was another connection between Geraldine and me. But what is it? Where is it? My mind races round in circles, but gets nowhere.

The picture of Lucy, which I can look at only briefly, has the same background. Lucy is sitting on the brick wall, wearing a dark green pinafore dress and a green and white striped shirt, white ankle socks and black shoes, her two thick plaits sticking out on either side of her head. She’s waving at the camera. At whoever was holding the camera…

Her father. The words pierce me like a cold needle. The man upstairs, whoever he is, is throwing away photographs of his wife and daughter. Of Mark Bretherick’s wife and daughter. Jesus Christ. And I allowed myself to feel safe around him, in his house.

I don’t stop to think. I yank the bag’s yellow drawstring and close it, without replacing the photographs. I’m taking them with me. I run to the door, out into the hall, and freeze, nearly dropping the pictures. He’s there, back in his chair in front of the stove. His head bent, gazing down at his lap. Has he forgotten I’m here? I stare in horror at the photographs in my hand, hanging in the air between us. If he turned now, he’d see them. Please don’t turn.

I unzip my handbag and stuff them in, pulling out my phone. ‘Sorry,’ I say, waving it in the air, a cartoon gesture. ‘My mobile rang and… I thought I’d take it in there. I didn’t want to… you know.’ I can’t do this. I can’t stand here with photographs of Geraldine and Lucy in my handbag and talk to him as if nothing’s changed.

My fingers tug at the zip but my bag won’t close. I hold it so that it hangs behind my body. If he looked closely he would see the edges of the frames poking out, but he hasn’t even glanced in my direction. There’s a pile of A4 paper on his lap. White, with print on it. That’s what he’s looking at. ‘I want you to read something,’ he says.

‘I have to go.’

‘Geraldine kept a diary. I knew nothing about it until after she was dead. I need you to read it.’

I baulk at the word ‘need’. In his chair, with his long legs crossed at the ankles and those pages on his knee, he looks harmless once again. Frail. Like a daddy-long-legs that you could brush with your hand and it would fall to the ground.

‘You haven’t asked me what I want.’ I inject what I hope is a reasonable amount of suspicion into my voice. ‘Why I’m here.’

His eyes slide to the floor. ‘Sorry,’ he says. ‘Bad manners. Bad host.’

‘Last year, I met a man who told me his name was Mark Bretherick. He claimed to live here, in Corn Mill House, and to have a wife called Geraldine and a daughter called Lucy. He told me he had his own company, Spilling Magnetic Refrigeration…’

‘That’s my company.’ A whisper. His eyes are sharper and brighter suddenly as he turns to face me. ‘Who… who was he? What do you mean, he told you? He pretended to be me? Where did you meet him? When?’

I take a deep breath and tell him an edited version of the story, describing the man I met at Seddon Hall in as much detail as I can. I leave out the sex because it’s not relevant. Just something bad and wrong I needed to do so that I could come home and be good again.

Mark Bretherick listens carefully as I speak, shaking his head every so often. Not in mystification; almost as though I’m confirming something, something he’s suspected for a while. He has someone in mind. A name. Hope mixed with fear starts to stir inside me. There’s no getting away from it now; he’s going to tell me something I’ll wish I didn’t know. Something that led to a woman and a little girl being killed.

I finish my story. He turns quickly away from me, rubbing his chin with his thumb. Nothing. Silence. I can’t stand this. ‘You know who he is, don’t you? You know him.’

He shakes his head.

‘But you’ve thought of something. What is it?’

‘Do the police know?’

‘No. Who is he? I know you know.’

‘I don’t.’

He’s lying. He looks like Nick does when he’s bought a new bike that costs a thousand pounds and he’s pretending it only cost five hundred. I want to scream at him to tell me the truth but I know that would only make him even more unwilling to talk. ‘Is there anyone you can think of who envies you, who might have had a thing about Geraldine? Someone who might have wanted to pretend to be you?’

He passes the bundle of paper across to me. ‘Read this,’ he says. ‘Then you’ll know as much as I do.’

When I look up eventually, once I’ve read each of the nine diary entries twice and taken in as much as I can, there is a mug of black tea on a slatted wooden table by the side of my chair. I didn’t notice him bringing either. He paces in front of me, up and down, up and down. I struggle not to let my revulsion show; this woman was his wife.

‘What do you think?’ he says. ‘Is that the diary of someone who would kill her daughter and herself?’

I reach for my drink, nearly ask for milk but decide not to. I take a gulp that scalds my mouth and throat. The mug is covered in writing: ‘SCES ’04, The International Conference on Strongly Correlated Electron Systems, July 26-30 2004, Universität Karlsruhe (TH) Germany ’.

‘It’s not the Geraldine I knew, the person who wrote all that. But then she says, doesn’t she? She’s got that part covered. “Whatever I feel inside, I do the opposite.” ’

‘She didn’t write it every day,’ I say. ‘From the dates, I mean. It’s only nine days in total. Maybe she only wrote it when she felt really down, and on other days she didn’t feel like that at all. She might have been happy most of the time.’

His anger surprises me. He knocks the drink from my hand, sending it flying across the hall, spraying tea everywhere. I watch the mug’s arc through the air, watch it fall on to the window seat as he yells, ‘Stop treating me like I’m mentally impaired! ’ I duck, making a hard shell of my body to fend off an attack, but he is already kneeling beside me, apologising. ‘Oh, my God, I’m sorry, I’m so sorry, are you okay? Christ, you could have got third-degree burns!’

‘I’m all right. Honestly. Fine.’ I hear the tremor in my voice and wonder why I’m rushing to reassure him. ‘It went on the floor, not on me.’