‘I see dead people,’ he says again, louder, hoping to attract laughter from nearby colleagues. I want to rip out his stupid goatee beard hair by hair.

No one responds.

Owen gets impatient. ‘Haven’t you all seen The Sixth Sense?’

We tell him that we have.

‘That woman that’s been on the news-Bretherick. The one who killed her sprog and herself-she’s a dead ringer for Sal, isn’t she? Spooky!’

I’ve never met anybody with a more irritating voice. Owen sounds, all the time, as if he badly needs to clear his throat. Every time he speaks you can hear the phlegm rattling inside him; it’s disgusting.

‘You will be dead soon if you don’t learn how to drive.’ He laughs. ‘Before, on the road. What was that all about?’ He is looking at his audience, not at me. He wants to belittle me in front of everybody. Like Pam Senior yesterday, yelling at me in the street. It must have been Owen who beeped his horn at me when I came to a standstill outside our building earlier.

‘Sorry,’ I mumble. ‘I’m tired, that’s all.’

‘It’s all right.’ Owen pats me on the back. ‘I’d be in a state too if I were you. You know, legend has it that if your doppelgänger dies, you die too.’

‘Is that a fact?’ I grin at him to show that his words have had no effect. Actually, that’s not true. They’ve made me feel more robust. Owen could never be anything other than utterly prosaic. Hearing him drone on about doppelgängers inspires me to pull myself together. So what if Geraldine Bretherick looked like me? Plenty of people look like plenty of other people and there’s nothing sinister about it.

I don’t dislike many people, but I do dislike Owen Mellish. He thinks he’s witty, but all his jokes are against other people. They’re jibes concealed behind a thin veil of humour. Once when I rang the office to say I was stuck in traffic and had been for nearly an hour, he laughed at me and said triumphantly, ‘I came in at sparrow’s fart and there was barely a car on the road.’

Owen is a sediment modeller, and unfortunately I have to work with him on almost every project I undertake. He creates computerised hydrodynamic models of sediment structures, and I can’t work without them. The programs he writes can apply any conceivable tidal or water change, natural or man-made, to sediment with any ratio of silt to sand to cohesive mud, any flock-size. It constantly annoys me to think that, without Owen and his computer, my work would be far less accurate.

At the moment he and I are working together on a feasibility study for Gilsenen Ltd, a large multinational that wants to build a cooling plant on the Culver Estuary. Our job is to predict future levels of contaminant concentrations and industrial enrichment, in the event of the plant being built. We have to deliver our final report in two weeks’ time, and Gilsenen has to pretend to care; it’s crucial to its image that it appears ecologically responsible. So I have to speak to Owen often, and hear his rattling voice, and I can’t get it out of my head that his wife had their first child only four months ago and two months later Owen left her for another woman. Now he takes his new girlfriend’s daughters to the park every weekend, and even has a photo of them on his desk at work, but he never mentions his own son, who was born with a serious heart defect. It’s a pity his computing expertise doesn’t extend to making a mathematical model that can assess the effect on a baby of being abandoned by his father.

‘ “To whom it may concern”.’ Owen’s looking at my screen, reading my words aloud. ‘What’s that? Making a will, are you? Very sensible. What happened to your face, anyway? Hubby been beating you again?’

I grab my mouse and try as quickly as I can to close the file I thought I’d already closed. Do I want to save the changes? In my flustered state, with Owen looking over my shoulder, I click on ‘no’ by mistake. ‘Shit!’ I open the file again, praying. Please, please…

There is no God. It’s gone. The draft of my salt-marsh article has been resurrected.

I push past Owen, out of the office and into the corridor. All that effort-gone in the time it took to press a button. Shit. Would I have sent it? I doubt any police force anywhere in the world has ever received a letter like it, but I don’t care-every word of it was true, and writing it made me feel better for as long as it lasted. I ought to go back to my computer and start from scratch but that’s a prospect I can’t face at the moment.

I try to focus on despising Owen but all I can think about, suddenly, is the red Alfa Romeo. Writing to the police was a way of pushing it aside. Now that my letter’s disappeared, I can’t avoid it any more.

I first noticed it on the way to nursery. It was behind me almost constantly, and all I could do was stare at it helplessly, worrying. Normally, car time is grooming and breakfast time for me, the only chance I get to brush my hair, put on my perfume, eat a banana. Today, I felt watched, and couldn’t bring myself to do any of those things.

I couldn’t see the driver of the Alfa Romeo because of the sun reflecting off his windscreen. Or hers. I thought of Pam but I knew this wasn’t her car. She drives a black Renault Clio. When I turned left into Bloxham Road, where the children’s nursery is, the Alfa Romeo went straight on. I was relieved, and even laughed at myself as I lifted Jake out of his car seat, while Zoe waited patiently on the pavement beside me holding her shiny pink handbag with pink and blue butterflies on it. My daughter is obsessed with handbags; she won’t leave the house without one. Inside today’s choice she’s got fifty-pence in ten- and twenty-pence pieces, a pink plastic car key and fob and a multicoloured plastic bead bracelet.

‘Nobody’s following us. Silly Mummy,’ I said.

‘Why, who did you think it was?’ Zoe asked, surveying the empty road, then scrunching up her face to examine me more closely.

‘No one,’ I said firmly. ‘There’s no one following us.’

‘But you thought there was, so who did you think it might have been?’ she persisted. I smiled at her, proud of her advanced reasoning skills, but said nothing.

I dropped the children off and, on my way out of the building, bumped into Anthea, the manager, who is in her mid-fifties but dresses like a teenager, in crop-tops and visible thongs. She gave me another dressing-down, twirling her long streaked hair round her index finger as she spoke. I’d been late to collect Zoe and Jake four days in the past fortnight, and I’d forgotten to bring in a new packet of nappies for Jake so the girls had had to use nursery spares when they changed him. Heinous crimes, both. I apologised, mentally added ‘Buy new nappies, try harder not to be late’ to my list, and ran back to the car, swearing under my breath. I had a lot to do at work today and didn’t have time for Anthea’s lectures. Why didn’t she just charge me for any spare nappies Jake used? Why didn’t she charge me extra if the staff had to stay longer on the days when I was late? I would happily have paid them double, or even quadruple, for that extra hour. I’d still only have had to write one cheque at the end of the month. I don’t care about spending money, but I get twitchy at the thought of losing even a second of valuable time.

On the way to the post office to post my anonymous letter to the police, I kept checking my rear-view mirror. Nothing. I’d got halfway to Silsford before I saw the red Alfa Romeo again. Same number plate. Sunlight bounced off the windscreen and I still couldn’t see the driver; a dark shape was all I could make out. I tasted bitter coffee in the back of my throat, mixed with bile.

I pulled over by the side of the road and watched the Alfa Romeo speed ahead of me and out of sight. It could be a coincidence, I told myself: I’m not the only person who lives in Spilling and works in Silsford.