It was late, much later than she had planned to get home, but it had been a good evening and for once she had really enjoyed herself. Jasmine Rogers took her mobile from her handbag before dumping the bag on the hall table. Shouldn't have had the coffee of course, it was back to work first thing tomorrow, or today, to be precise, but she was always faintly nervous around other people's dinner tables and it was good to have something to hold on to, a glass of wine, a cup of coffee, a cigarette. No one smoked anymore of course, she was the last of her friends to have given up and it was at gatherings like tonight's when she longed to be able to reach for a cigarette. She was glad there were none in the house right now, the urge was so strong. In the sitting room by the sofa she kicked off her shoes – you were seventy per cent more comfortable with your shoes off, she had read somewhere – and went into the kitchen without bothering to turn on the light. Jasmine had lived in this tiny two-bedroom house for twelve years now and was sure she could navigate every inch of it blindfolded. Having filled a tall glass with water from the tap she greedily drank from it, then refilled it. She'd had too much wine too and hoped the alcohol would win over the caffeine once she got to bed. There was nothing worse than ... than ...

A sudden feeling of unease appeared as if from nowhere. She lost the thread of her thought and stopped halfway to the door. Standing very still in the dark she sniffed the air. What was that smell? A strange smell. No, not strange, unfamiliar. A smell that didn't belong here. A faint whiff of something like cheap aftershave or air freshener. Perhaps she had brought it with her from the party though she didn't remember smelling it there. Did she carry it with her from the minicab? That certainly had smelled of all sorts of things, some best not too closely analyzed.

Jasmine tried to shrug off the feeling of unease and left the dark kitchen. She carried her glass of water, a nightly ritual, to the bottom of the stairs where she flicked off the downstairs lights. Just as she did so an after-image of the little dark wood mantelpiece tugged at her eyes and once more made her stop in the dark. Was something missing there? She flicked the light back on and went to examine it.

The house was sparsely decorated and there were few ornaments – you had to show restraint in a house this small – and the same five items, dutifully dusted once a week, had stood on top of the mantle for years: a tiny fake bronze of a satyr brought back from Crete; a heavy lump of pink quartz inherited from an aunt; a black ceramic candle stick holding a red candle she never lit; a framed picture of her younger self cuddling a dog now long dead; and a hand-carved wooden bowl with a rose motif around the rim, always empty. It was all there, all five items.

Then why did it make her feel queasy to look at them? Perhaps she was more drunk than she realized. A sip of water. She didn't really feel sick, it was more a mental queasiness, like having been asked an urgent question in a language she barely understood. She tore herself away, turned off the lights again and this time climbed the short stair, automatically avoiding the spot that creaked on the third step from the top.

On the narrow landing she halted and sniffed again: those refreshment towels soaked in eau de Cologne that you got with finger food? As always she had left the narrow window on the landing ajar since all the kitchen odours seemed to waft upstairs, so perhaps that was how the smell had drifted in. In her bedroom – she used the smaller, quieter one in the back – she undressed. What a relief. The place felt stuffy. It was unnaturally mild for the middle of March but she just knew that the moment she turned the heating off the weather would turn icy again. She flicked off the light and opened the window a crack to let in some air. Below, quietly, almost imperceptibly, her little low-maintenance garden was awakening in the mild air. Yet even here at the window she thought she could smell the faint, alien perfume. She had it in her nose now, she supposed, no point in obsessing about it. Living alone could turn people peculiar; she always worried about that, worried she was becoming eccentric. Peculiar habits. Obsessions. Talking to yourself.

'Talking to yourself,' she said aloud to her reflection in the bathroom mirror. The buzz of her electric toothbrush was loud in her ears, drowning out the little night noises. She was glad this was a quiet neighbourhood – quiet for Bristol, anyway – and her neighbours on both sides elderly. Never a noise. Probably asleep since ten. As she replaced the toothbrush on its holder the smell came strongly into her nostrils. She had it now: deodorant. All-over body spray. One of those things that made men irresistible in television adverts. Someone out there must have seriously overdone it.

She padded back into the bedroom in the dark and slid into bed. The sheets were cool on her skin but that wouldn't last. She really liked her days warm and her nights cool. Lying on her back she plucked the blanket loosely around herself and closed her eyes.

With the window and the door to the landing open a tiny breath of air stirred from time to time, caressing the skin on her exposed arms. Forty-six years old and all that touches me is the wind. Don't go there, or you'll never sleep. She reached for her glass of water, always in the same place so she could find it in the dark.

The mantelpiece. Jasmine shot upright, pulled the bed sheet up to her neck and swung her legs out of bed. She knew now. The phone, the phone, where was her mobile? Now she knew there was someone in the house. It didn't come from outside, the smell was here, on the inside. Because someone was here. Her feet tangled with the bed sheet on her flight to the door where she ripped her dressing gown off the hook and frantically struggled into it. She couldn't smell it now but she knew someone was hiding. The proof was downstairs. Why did she leave her phone there? Never let your phone out of reach, it's not safe, not even in your own house. Irresolute she stood on the landing. The spare bedroom. Its door was closed. He had to be in there. It was the only place she hadn't been in tonight. Her nostrils flared as she tried to sniff out the intruder. He was waiting in there. Get to the phone. Downstairs. Get to the phone. Holding her breath she backed away from the closed door to the top of the stairs. With infinite care she let herself down along the handrail, backwards, avoiding the stair that creaked, step by step, down to the bottom. Her hand fluttered as she groped for the light switch, never taking her eyes off the top of the stairs.

She forced herself to look at the mantelpiece again, eyes wide, unblinking. Her stomach contracted into a twisted ball of fear. Yes, there were the same five ornaments that had always been there. But the order had been reversed as though she was looking at it in the mirror. Her eyes sought other surfaces. The top of the television: ceramic dog and glass paperweight, reversed. The bookshelf: pine cone, sea shell and Moroccan lantern, wrong way around. Even the cushions on the sofa: swapped over. The telephone on the writing desk by the window looked miles away. She felt she might never...