Memories fall into two categories. There's the sort you carry on your person all the time, such as keys and coins; and there are the random images which float back now and then, biting and pervasive, impossible to ignore. And of these last, the dead

have their own particular pull.

It's a rainy Sunday night and we are propped in bed watching the OJ Simpson trial on BBC2 when she barges without warning into my head. Why now? Is it the ice-cream? (For the uninitiated, a tub of the stuff was found melted at the scene of the OJ crime.) Whatever it is, suddenly Iris Morgan, maker of ice-cream and dead these 21 years, pops up and says hi.

My partner sees me stiffen. "What is it?" he says.

"Nothing. I just remembered something." And we go back to watching the inscrutable Judge Ito and his egg-timers.

Like a tourist between towns, Iris hangs around all week - just bumming, just there, a face floating in my head. This persistence is true to form. She was (I think) in her forties when I knew her but, as far as I remember, she never did say please or thank you or wait her turn.

When I was 13, we moved to a steep, leafy road in the city centre, on the edge of the five-acre cemetery and the red-light district. Our house had gothic turrets, a billiard room, a Victorian grotto, crumbling walls. My mother painted the hall baby

blue and the sitting room Chinese yellow and single-handedly purged the house of its shadows.

My sisters, stepbrothers and I practised handstands in a garden strewn with rubbish chucked over from the street. It was a matter of hours before Iris knocked on our heavy, warped black door: "I love seeing their five pairs of feet over the wall," she told my mother. "Send them round for ice-cream - all or some of them, I don't mind."

It was her first order. We obeyed. Iris had the reddest, crinkliest hair we had ever seen. She sat us around he long oak table and gave us ice- cream in bowls thin as shells. She said she'd spank us if we broke them.

She told us she'd been brought up in the Far East and forced to eat raw liver at school, and that she'd been "a beauty" (photos bore this out). When my littlest sister remarked that she wasn't any more, Iris gave her a look which would have turned a less innocent heart to stone.

That summer, Iris sat in the garden all day in her bra sun-bathing, which she confided was bad for redheads. She smoked and wore a lot of purple and her confidence made us feel both more and less important.

We rarely saw her husband, Trevor, a GPO engineer who wasn't allowed to talk about his job. "He's the sort of man who might turn out to be a spy," my mother said. "There's something fishy about the whole set-up."

They had no children of their own (mother: "it figures"), but amicably shared their house with a ghost named Maud who appeared on the landing now and then with a pile of laundry. "She's just been," Iris would announce as she rummaged in the deep freeze. "You just missed her. A great pile up to here," she'd demonstrate, touching the bridge of her nose. And we'd shiver, though she was the one up to her elbows in ice.

There were various fallings-out with Iris. Once, for some dark reason of her own, she purposely tore my nine-year-old sister's scrapbook. She said she couldn't see what the fuss was about, but we knew she was lying.

Another time, our parents went for dinner at her house and my stepfather accidentally splashed red wine on her damask tablecloth and Iris was so abusive to him that my mother insisted they leave. "She thinks she's so fascinating," my mother fumed, "but in fact she's just plain bloody rude." After the cooling off, she'd come knocking and we'd be back for more.

I don't remember what sort of cancer she got, but the idea that Iris was actually going to die - right there next door - was a searing shock. It wasn't that she was an especially good person, but she had a big effect. She'd perfected the art of shaking up other people's lives; she was the most noticeable (and manipulative) person I knew.

The last time I saw her, she was sitting up in her big white bed at home, yellow-faced and snarling. Her hair was drained of its colour, like a dead flower. Every irritable comment she made, we accepted, absorbing the blows as though she were dead.

A month later we moved, to a better area. There was a cherry tree in the garden and five boys next door. I got my first Mary Quant bra, and the weather grew warmer. By the time Iris died a week or so later, we'd emptied our packing crates and switched our allegiance and she was already in the past.

That was 21 years ago this spring and I'd never have believed that she'd still haunt me now. Iris Morgan seems to live on in my head thanks to sheer bloody-mindedness - as if she knew very well that if she let go for a split second she'd be forgotten. Go on, she hisses at my elbow, write about me in a newspaper, make me real. And she shrieks her approval as, without hesitation, you and I comply.