As I hold the binoculars to my eyes, the wind whips through my hair, and I see the thing I have been waiting for, and dreading. On the mainland, heading in my direction, is a white car. I follow its progress for a few seconds. In a couple of minutes, it will cross the causeway and stop while the passenger gets out and opens the gate. It will move forward a couple of metres, and wait for the passenger to close it again.

I know the men who are inside. I met them both in the pub last week. In fact I knew the younger one years ago, when I used to come to the island as a child. Then he was skinny, with permanently scabby knees. Now, he's quite handsome. They were both friendly to me last week, but they won't be friendly now. Usually I love having visitors. It's a rare event, and it breaks the solitude. It stops me thinking about what I've done. I do not, however, plan to welcome these guests. They are the police, and they have come to arrest me.

I knew it would happen sooner or later. In a way, I am almost relieved. I have no chance of getting away, but my instincts still urge me to try. I've got this far. I have hung onto my freedom, and I won't give it up without a struggle. I’ll be in trouble for the rest of my life. I rush inside and wrap myself up in coats and scarves.

I give myself a quick glance in the hall mirror, as if anyone here cares what I look like. I never wear make-up now, but I seem to look better without it than I did when I was dolled up for work in London. I examine my messy hair and pasty face. I look young, and innocent. I am neither.

'Floppy!' I call, as I run down the stone steps, two at a time. 'Skip!' I add, just in case.

Normally my dog comes running as soon as he hears either of his names. I don't know where he's gone. I shout a few more times, and then set off on my own, half running to get away in time. I rush downhill to the edge of the island, staying where I can't be seen from the road. I am aware, all the time, that my flight is futile. I can't get the image of what I did out of my head. She looks at me. She is horrific. I never saw her, but I can imagine it.

I make myself concentrate on my surroundings. This island is spectacular. The grass is mossy and green. The sky is invariably cloudy, and the soft light heightens everything. I breathe the cold, fresh air and appreciate it. I might not be breathing it for long. Dry stone walls criss-cross the fields. The sheep get up and walk away, with dignity, whenever I lurch in their direction. Flop, wherever he is, is always kind to the sheep. I wonder whether a London dog, abruptly relocated, thinks he's died and gone to heaven. There are no scrawny poodles rushing up to smell his bottom, and he has the run of the entire island. Sometimes I watch him leaping around on the hillside, going crazy. Once he tried to swim in the loch, but it was too cold for him. It will, however, be spring next month.

It will be spring on the island, but that will make no difference to me. I notice I am shaking. By spring I’ll be in Holloway Prison¹, and Flop will presumably be back with Stuart and Alison. I wince as her name comes into my head. I can hear the car driving faster than advisable over the stones. I should have got a boat for when this happened. I wonder idly where the dog is. As I scramble down to sit at the water's edge, I realise that it was probably Skipper's new name that led to my downfall.

When Stuart dumped me², we both wanted the dog. We each thought we had a claim. I'd adopted him from the shelter, but Stuart had housed him. I'd walked him, but Stu had paid for his food. I kidnapped him from Stuart's house, without leaving a note. Stuart and Ally turned up on my doorstep the following weekend, and demanded him back. They came together just to taunt me. She was looking rangy and elegant. If I'd known she was coming, I'd have brushed my hair, but I knew I couldn't compete. I hated her. I couldn't believe she had the nerve to come to my flat.

We all stood awkwardly in the kitchen, and I showed them the way the dog answered to his new name. Stuart looked at me with something like pity, and said 'My God! You're a psycho!' They both laughed, shook their heads, and left. I suppose I'd shown them my true colours. I'd been the doormat for years. If I'd kept it up a little bit longer, I might not, now, be running away from the law. I should have sacrificed the dog.

My stomach is scrunched into a ball. I didn't mean to do it. This has been my mantra for the past ten days. I don't know whether that makes it better or worse. I didn't mean to do it; but I meant to do something. I wanted revenge, and I suppose I have got it. A life is ruined, and I should be glad.

I don't know how my relationship with Stuart led to this. I used to think our biggest problem was the fact that we worked together. Our colleagues loved him and hated me, but we didn't care. We loved each other. We had happy Sunday mornings, reading the papers and eating toast in bed, while Skipper (Floppy) lay across our legs. Stuart could talk for hours about Crystal Palace's hopes of promotion (lack thereof) or about rare plants. He was a horticulturist, by training. A horticulturist stuck in an office job. We would stand by his front window and look at his hedge. It was his pride and joy. He adored his rare shrubbery. He would talk, and I would listen, because that's the kind of woman I am. I am quiet. I'm a good listener.

I'm boring. That's what they used to say in the office, because I could never be bothered to talk to them. They'd sneer at me, and talk about me, and because I was so quiet, they'd forget they were within earshot. I've always held myself back. People have overlooked me since my first day at nursery school. The mistake people make is to assume that just because someone's quiet, they are necessarily good. The world at large sends quiet people to the bottom of the heap, assuming that they are lacking in confidence, that they are shy, that they want to be liked, that they are eager to please and therefore easily dismissed with contempt. No one would think to feel threatened by me.

I sit beside a rock. It's a big rock and I hope it might screen me. The air is bitterly cold, and I huddle into myself. By now they will be inside the house. I never lock the door. No one does. The police are in my house, looking for me. They are ready to arrest me. If the dog comes home, they'll ask him where I am. He might help them look for me. He'll be able to smell me. He'll help them find me. I throw a stone into the water. Treacherous Mr Floppy

I disliked Ally from her first day at work, but it took me a while to notice that she was stealing my boyfriend. I knew she was taller, slimmer and prettier than me, but I despised her because she was self-consciously bubbly. I could see through her, so I imagined Stuart could too. She was desperate to be liked. I could see how insincere she was.

'I’m going to the canteen,' she simpered to Stuart, in her second week. 'I need a chocolate boost. Not to mention a packet of fags³. Can I get you anything?'

'Oh, no, cheers,' he said. 'I’m not a chocolate fan. I prefer savoury things myself. And I definitely don't smoke.'

'Oh, me neither,' she said, performing an inept U-turn. 'At least, I'm quitting.'

And off she skipped. When she came back, she'd bought them each a packet of salt and vinegar crisps.

Then Stuart started dropping her name into the conversation, on almost any pretext.

'Shall we go to France at Easter?' I asked him, about a month ago.

'OK. You know, Ally was saying she grew up in France. She speaks perfect French. I got her to say something for me, and she really did sound like a French person.'

'Well you don't speak French, so it's easy for her to impress you.'

'No, she went to school there and everything. She even has that weird curly handwriting they have abroad. Really, you should ask her to say something. Being bilingual is such a blessing. I'd love my children to be bilingual.' He hastily corrected himself. 'Our children.'

I told myself that he was just infatuated, that she probably had a boyfriend, that it didn't mean anything.

I knew I was wrong on all counts. He fancied her, and she fancied him. It was staring me in the face. I noticed it and everyone else noticed it too. They loved it. It had all the ingredients of the perfect office scandal: boyfriend of unpopular girl goes off with gorgeous, lithe, friendly girl. Unpopular girl is humiliated. Friendly girl is triumphant. Office is bitchily happy.

I became tense. I didn't want to be dumped. I started asking him about her, pestering him, demanding answers.

'Of course I fancy her,' he admitted, warily. 'Everyone does. She's gorgeous. That doesn't mean I don't love you. Everybody looks at other women. It doesn't mean anything.'

'Well, what would you do if she came on to you?'

'I'd never cheat on you, if that's what you mean.'

'What if she was persistent?’

His eyes lit up. 'I suppose I'd just be flattered and walk away.'

He was lying. I knew he was lying. He knew that I knew he was lying.

I throw another stone into the water, and stare out to sea. There is no way I can escape now. When it happened, it came in an irresistible whirlwind. It was almost comically predictable. I came to Scotland to visit my parents one weekend. It's not something I particularly enjoy, but it has to be done from time to time. Leaving Stuart for two days felt wrong, but I knew I couldn't stay by his side for ever, just to ensure his fidelity.

As I left the office on Friday afternoon, I watched Stuart and Ally flirting. I'd brought my weekend bag with me, and by the looks of things, one of them should have done the same. He was standing by her desk, talking to her, leaning forward, being overly attentive. She was looking into his eyes and giggling. They both looked as though their next logical step was to rip each other's clothes off. I seethed, and didn't say goodbye.

Sometime during the weekend, he'd pushed a note through my door. I had expected to be asked out for a drink or something else ominous. I hadn't expected to be given my marching orders on a scrappy piece of paper torn from his filofax⁴. He didn't mention her name, either out of a misguided attempt to avoid hurting me, or, more likely, through cowardice. It was not a friendly letter. Three years, and that was all I got.

It still pains me, although I know I've cancelled my entitlement to feel wronged. At the time, I was in agony. I'd been half expecting it for weeks, but I still wasn't prepared for losing Stuart.

I sat down in my kitchen, and crumpled the note. I poured myself half a pint⁵ of whisky. I straightened the note out again, and smoothed it down. I read it. It hadn't changed. I knocked back the whisky. I hated him. I hated her. I realised I had to be at work in twelve hours, and that they would both be there. Everyone would know. I decided to resign.

So I went to the office, just to check that the obvious was, indeed, the case. I put on my best, red suit, and more make-up than usual. I kept my chin up, and fixed grin to my face. When I walked over to my corner, everyone went quiet. They looked at me, and I caught a few sniggers. They were so predictable.

I looked around. Stuart was at his desk, head down. He knew I was there, but he wasn't making eye contact. Ally was there too - of course she was; they must have come in together. She caught my eye, and looked away quickly with a small smile.

'Good morning, Alison,' I said loudly. She mumbled something.

'Morning, Stuart,' I added. 'Thanks for your scrap of paper. Very gentlemanly. I’ll have the dog.'

I got a laugh, and for a few seconds I was triumphant. Then I was wretched. I didn't want him back, but I was humiliated.

I left work at lunch time, and I never went back. I knew they weren't going to bother to take me to court. I wasn't important enough. I stayed at home for a while, fuming. I wondered why he had said he loved me, if he didn't mean it. I wondered why I'd let myself get so involved. I'd never done it before. I might not do it again.

As the days went by, I disgusted myself by acting like a parody of a woman scorned. I sat around in my pyjamas, writing him furious letters and throwing them into the bin, while Richard and Judy murmured platitudes in the background. I went to his house while he was at work, and took the dog. Some piece of faulty wiring in my brain made me decide that if I renamed Skip, everything would be all right. Mr Floppy kept me company, but he didn't make me feel any better. I came to realise that I would only be able to, overcome my rage by unleashing it. The more I thought about it, the more logical it seemed. All I needed was to exact some fleeting revenge on them. They wouldn't know it was me, but I'd know that I'd caused them anguish of some sort, and that would be enough. Then I'd be able to get on with my life, such as it is. My jobless, friendless life. That was when I decided to come to Scotland. I'd cause Stuart some misery, and immediately afterwards, I'd drive north. I ascertained that my great-aunt's⁶ cottage was available, and that the key was under the stone.

I made a plan. I would set Stuart's precious hedge ablaze while he was in his house with Alison. They'd be scared, they'd call the fire brigade, they'd be fine, and the rare and wonderful hedge would be ruined, by which time I'd be miles away.

I drove out of town, so no one would remember me, and bought a small container of petrol. At ten-thirty one night, I poured it generously over the leaves. They were drenched. I was excited. I had a box of matches in my pocket, but the house was empty. I knew Ally lived in a shared house, so I was banking on them staying at Stuart's. They’d come home soon - they'd have to - and then all I had to do was walk past, toss a lighted match over, and move swiftly away. I knew that I could cut through the alleyway two houses along, and be on the main road within seconds. Normally I would have avoided the passage, in case I met anyone dodgy, but in this instance I was the evil one, and I calculated that the chances of there being two of us about were remote. I was hugging myself in anticipation. I wanted to bring Floppy with me, but I feared he'd give me away, so I made him wait in the car, with all my possessions.

Soon, I saw them coming down the street. He was holding her hand. This sent a hot wave through me. He never, ever used to hold my hand in public. He just didn't want to.

'Hey, don't think it's because of you,' he once told me, when I complained.

'Why is it, then?'

'Public displays of affection just aren't my thing. That's all. Never have been. Nothing personal.' He rumpled my hair. And now here he was, with Ally's skinny hand in his. She was tottering along on high heels. I caught a good glimpse of her pretty face in the light of a street lamp. I knew she smoked, but I never gave it a moment's thought. I knew that Stuart was bitterly opposed to anyone smoking in his house. I should have realised what might happen. It came as a complete shock. I was hidden in the shadows across the road, wearing black. I was waiting for them to go in so I could make a pretty conflagration, and get into my car, which I'd parked at the top of the alley.

It happened quickly. She said something to him, and stopped. He walked on, and put his key in the door. She took out a packet of fags, and leaned into the hedge to get out of the wind. A second later, she went up in flames.

I ran. I woke up in a nondescript hotel at some motorway services near Leicester⁷, with Floppy curled up in a corner, and I turned on the radio. I hoped it would be a dramatic enough story to make the national news, and it was. She was alive, but she'd lost her lovely face. She was covered in burns. She was in intensive care. I got in my car, and drove as fast as I could towards my new life, as she began to come to terms with hers. I reflected that this would test their great so-called love, and then I remembered that they'd never claimed to be in love at all. I tried to tell myself she deserved it for stealing my boyfriend, but I knew she didn't. I tried to banish the knowledge that it was entirely my fault. I thought I might get away with it. My trump card was the fact that I was so meek. No one would even remember that I used to go out with him.

I cannot feel triumphant, however hard I try. When I close my eyes, I see her lovely face, lost for ever. I try to picture it covered in burns. I cannot believe I did that to someone. It's funny how fine is the line between good and evil. You go through life with yourself firmly marked down as good and law abiding and sinned against. With one easy act, you shift yourself straight into the other column. You become a criminal. I am an accidental perpetrator of grievous bodily harm⁸.

I've known all along that the police would come for me. I have been dwelling on the miracles of forensic science. It's not easy to get away with things. They know someone poured petrol on the hedge. The consensus seemed to be that it was random vandalism, but I can’t assume it's going to stay that way. There must be ways that I've never even thought of for them to identify me. You always leave a trace. Apart from anything else, I had a motive.

It could be the fact that I changed the dog's name. Where is that bloody dog? It could be that I left a hair at the scene. It could be that someone saw a short woman in black running down the alleyway and leaping into a car. It could be anything. The chances are, however, that they don't actually know it was me. I'm going to have to be clever with my answers. They'll make me go to London. I'll be back in the city, breathing the foul air. I'll go to prison. People will only want to talk to me in the same way they want to talk to Myra Hindley⁹, so that they can tell people they met me. No one will want to be my friend, except the sick people who fall in love with people in prison, and that only works when it's the man who's incarcerated. Men are too practical to kid themselves that they're in love with an evil witch like me.

I am crouched at the water's edge, in a futile attempt to be invisible. I hear their footsteps, and I know I'm doomed.

'There you are!' says the younger policeman, Robbie. He seems to be smiling. I wonder how he'll tell the story of the day he discovered the village had a psychopath on its outskirts.

'Hi,' I tell him, weakly.

The older one speaks.

'We've looked all over for you,' he says. 'I’m afraid we've got some bad news.'

I force myself to look at him. 'What?'

'It's your wee¹⁰ doggie. He's been run down.'

'It was an accident,' adds Robbie. 'The postman's terribly sorry.'

'My wee doggie? Mr Floppy?' Poor Floppy. He'd never deserved that name, and now he's dead. 'Is that why you came?'

I live in a village where the police solemnly inform you that your dog is dead. In London he'd have been scraped off the tarmac by unscrupulous restaurateurs by now.

'That's terrible news,' I add. Mr Floppy has been sacrificed so that I may walk free. I am not going to prison. Not yet, at least. I can't take it in.

I look at the police, trying to remove all traces of guilt from my features. Robbie smiles sympathetically. I realise that he's not exactly spoilt for choice round here when it comes to the ladies. I think I've known all along that the best revenge I could ever exact on Stuart would be to have a happy life without him. Perhaps I am beyond revenge now, but I might try to do it anyway. It might ensure my continued freedom.

'I’m going to have to pour myself a drink,' I say loudly, startling myself. 'Will either of you join me? And, um, do you have the ... body?'

Two hours later, a slightly drunk young policeman is digging a grave outside my cottage. Floppy has gone, and now I have Robbie. He's grown up well, since he was a scabby-kneed boy. He's going to get me a puppy. He and I seem to get on well. I vow to give it my best attempt.

If any other woman looks at him, I think I’ll be able to sort her out.