‘I’m so sorry. I don’t know what to say. God knows what you must think of me now.’

I feel dizzy, trapped. ‘I didn’t mean to make you angry,’ I tell him. ‘I was trying to find something positive to say. The diary’s horrible. You obviously know it is, and I didn’t want to make you feel worse.’

‘You couldn’t.’ His eyes seem to issue a challenge.

‘Okay, then.’ I hope I’m not about to break my own personal stupidity record. ‘Yes, I think this is the diary of someone who might kill her daughter. No, I don’t think it’s the diary of someone who would kill herself.’

He watches me closely. ‘Go on.’

‘The writer… the voice throughout seems to be screaming self-preservation at all costs. If I had to guess what sort of woman wrote it, I’d say-look, this is going to sound awful.’

‘Say it.’

‘Narcissistic, spoilt, superior-her way of doing things is better than everyone else’s…’ I bite my lip. ‘Sorry. I’m not very tactful.’ A ruthless ego, I add silently. Someone who starts to see other people as worthless and expendable as soon as they become obstacles to her getting her way.

‘It’s all right,’ says Mark Bretherick. ‘You’re telling me the truth. As you see it.’ For the first time, I hear a trace of anger in his voice.

‘Some of what she’s written is exactly what I’d expect,’ I say. ‘Being a parent can be massively frustrating.’

‘Geraldine never had a break from it. She was a full-time mum. She never said she wanted a break.’

‘Everybody wants a break. Look, if I had to look after my kids full-time, I’d need strong tranquillisers to get me through every day. I can understand her exhaustion and her need to have some time and space for herself, but… locking a child in a dark room and letting her scream for hours, pulling the door shut so she can’t get out, and that stuff about having to make her suffer in order to feel protective and loving towards her; it’s sick.’

‘Why didn’t she ask me to hire help? We could have afforded a nanny-we could have afforded two nannies! Geraldine didn’t have to do any of it if she didn’t want to. She told me she wanted to. I thought she was enjoying it.’

I look away from the anger and pain in his eyes. I can’t give him an answer. If I’d been Geraldine, married to a rich company director and living in a mansion, I’d have ordered my husband to stock up on a full team of servants the instant I emerged from the maternity ward. ‘Some people are better than others at asking for what they need,’ I tell him. ‘Women are often very bad at it.’

He turns away from me as if he’s lost interest. ‘If he can pretend to be me, he can pretend to be her,’ he says, blowing on his cupped hands. ‘Geraldine wasn’t narcissistic-the very opposite.’

‘You think someone else wrote the diary? But… you’d have known if it wasn’t Geraldine’s handwriting, wouldn’t you?’

‘Does that black print look like handwriting to you?’ he snaps.

‘No. But I assumed-’

‘Sorry.’ He looks disgusted, mortified to find himself having to apologise again so soon after the last time. ‘The diary was found on Geraldine’s computer. No handwritten version.’

There’s a sour taste in my mouth. ‘Who is William Markes?’ I ask. ‘The man she said might ruin her life?’

‘Good question.’

‘What? You don’t know?’

He barks out a laugh without smiling. ‘As things stand, you know more about him than I do.’

My breath catches in my throat. ‘You mean…?’

‘Ever since I first read that diary, I’ve had a name in my head with no one to attach it to: William Markes. Then out of the blue you turn up. You’re Geraldine’s double, physically, and you tell me you met a man who pretended to be me. But we know he wasn’t. So at the moment we’ve got no name to attach to the man you met in the hotel.’ He shrugs. ‘I’m a scientist. If I put those two facts together…’

‘You come to the conclusion that the man I met last year was William Markes.’

Sometimes, convenience has the appearance of logic: you link two things because you can, not because you must. I’m also a scientist. What if the two unknowns are unrelated? What if the man at Seddon Hall lied because he was breaking the rules for a week and wanted to cover himself, not because he’s a psychopath capable of murder?

If William Markes, whoever he is, faked Geraldine’s diary after killing her, why did he include his own name? Some kind of complicated urge to confess? Being a scientist and not a psychologist, I have no idea if that’s plausible.

‘You need to tell the police. They’ve given up looking for William Markes. If they hear what you’ve just told me…’

I am on my feet. ‘I’ve got to go,’ I say, pulling my bag out from where I left it behind the chair. I wrap my arms around it so that he doesn’t see the frame edges. ‘Sorry, I… I’ve got to pick up my kids from nursery at lunchtime today, and I’ve got some shopping to do first.’ A lie. Tuesday and Thursday are Nick’s days, the days when bags go astray and bills and party invitations vanish into thin air.

I have never, not once, collected Zoe and Jake at lunchtime. Their gruelling nursery regime is one of the many things I feel guilty about.

‘Wait.’ Mark follows me across the hall. ‘What hotel was it? Where?’

I pull open the front door, feel more real as the fresh air hits my face. It’s sunny outside, only a few feet from where I am now, but still the light looks far away. ‘I don’t remember the name of the hotel.’

‘Yes, you do.’ He looks sad. ‘You will tell the police, won’t you?’

‘Yes.’

‘Everything? The name of the hotel?’

I nod, my heart tightening with the deception. I can’t.

‘Will you come back?’ he asks. ‘Please?’

‘Why?’

‘I want to talk to you again. You’re the only person who’s read the diary apart from me and the police.’

‘All right.’ At this point I will say anything I have to if it means I can leave. He smiles. There is a hardness in his eyes: not pleasure but determination.

I have no intention of ever returning to Corn Mill House.

I drive to Rawndesley, feeling shell-shocked from my encounter with Mark, needing to forget everything to do with him, with what’s happened. In the Save Venice Foundation’s office, I spend several hours trying and failing to sort out the mess that Salvo, Vittorio and the TV producer have, between them, created. Natasha Prentice-Nash doesn’t comment on my bruised face, nor does she thank me for coming in on a Tuesday or apologise for landing something on me that shouldn’t be part of my job purely because I’m the only person in the office with basic social skills. By five o’clock I can’t stand it any more, so I head for home.

There’s no one there when I get back. Looking up through the car window, I see that our lounge curtains are open. Normally at this time they’re closed, with the warm glow of the lamp behind them so that Zoe and Jake can watch whatever CBeebies has to offer without sunlight interfering with the picture.

I climb out of the car, dragging my handbag after me, and look up and down the street for Nick’s car. It’s not there. Even so, I shout out my family’s names as I let myself into the flat. I look at my watch: quarter to six. Maybe the children are still at nursery. Nick might have left work late. Not that he’s ever done that in all the years I’ve known him. It must be nice, I’ve often thought, to have a job like that.

A horrible possibility occurs to me. What if Nick’s forgotten he’s supposed to be picking up Zoe and Jake? No, he’d still be back by now. He’s never later than five thirty. All I want is to come home to my normal messy, noisy house, two boisterous children and a husband holding out a glass of wine. So where are they?

I run upstairs to the kitchen. My stomach twists with worry when I see there’s no note on the table. Nick always leaves a note; I’ve finally managed to drum it into him that I worry if I don’t know where he is. At first he said things like, ‘What’s there to worry about? I mean, I’m obviously somewhere, aren’t I?’ Zoe and Jake are obviously somewhere too; the problem is that it’s not at all obvious to me where that somewhere is, and that’s not good enough.