Having left Oxford and gone to the US, academic Andrea Ashworth found herself overwhelmed by the past. She tells Harriet Swain how writing a chilling account of her violent childhood helped lay the ghosts to rest

Andrea Ashworth has enormous eyes. Spend time in her company and you know there is plenty going on behind them.

Read a few pages of her first book Once in a House on Fire and you realise they have seen a lot too - the green and purple bruises around her mother's eyes; her first stepfather sliding his fingers under her blankets as she pretended to sleep or holding a carving knife to her mother's cheek while smashed plates lay against the tiles; her second stepfather trying to wave goodbye wearing a pair of handcuffs and later, after his prison term for theft, with a big marble ashtray raised in his fist; her mother on tranquillisers threatening to end it all.

Those huge, dark, almond eyes sucked it all in from the age of five, when her father was found drowned, until she left to start life as an Oxford undergraduate 13 years later. Then - after studying for a year at Yale, a stint in Boston on an academic journal, a bohemian spell in New York's SoHo district as the eyes and hands of an 80-year-old artist and now a junior research fellowship at Jesus College, Oxford - she wrote it all down.

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The result is a chilling account of a poor childhood in Manchester, slashed by domestic violence. It is written through the eyes of a child in a series of vivid pictures. She describes wandering through Manchester's Indian district with her mad grandmother "stopping at Indian sweet shops and jewellery stores and delicatessens where flies buzzed around splits in rotting fruit too strange to buy". She tells of hot days in Canada where her family emigrated for a while, trying to stem her mother's migraines by drawing the curtains, which were "a dull red-orange, like a rotten sunset" and, back in Manchester, of truanting from school and huddling from the rain under "the burnt-out bandstand or in the huge concrete drains that tunnelled under the grass". When planning the book she began jotting down memories on index cards. "It would be a smell or an expression on someone's face," she says. "I was hoarding the memories, afraid that if I didn't scribble them down they would desert me. That was cathartic. I felt I held them in a box like jewellery."

Writing was not easy. The book was conceived when she went to the United States after Oxford and found herself suffering from vertigo every time she looked back on her life and tried to work out how she had got there. "Part of me is programmed to wake up and feel fear and worry about what mood people are going to be in and what happened in the night," she says. She tried writing short stories, but her past seemed to get in the way: writing a memoir was more than an idea, she says, it was a need. She set down the first two chapters in two weeks in Boston. A version was printed in Granta and a publishing deal followed fast. Back in Oxford, she finished her doctoral viva one week and started the book the next. The next two months were, she says, "two of the scariest of my life, including the life I was trying to describe. When I was growing up, I had the adrenalin to push me through. But this time there was a great premium on my writing because I had made sacrifices to do it. It was painful."

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Sitting, surrounded by people and plastic shopping bags, sipping a caffe latte in a crowded Oxford cafe bar, she discusses the horrors of her life with a disconcerting openness and zest. Dark and fine-featured in a black leather jacket and knee-length boots, she talks as she writes - fluently, in a series of vivid phrases and with a kind of wonder at being alive. At school, her dark skin prompted some children to call her "Paki". But mostly, she was known as "Smiler" because she always seemed so cheerful. Forced to keep her head down at home, she snatched at the merest hint of support from outside and, always outgoing, made friends easily.

Many of her worst experiences were hidden. The first time the infant Andrea realises there is something strange about her world is when a girl at school asks why her mum wears sunglasses all the time. Both stepfathers disliked strangers "knowing their business" and most people, from neighbours to policemen, looked away. Andrea's book forces readers to open their eyes. She does not think of it as being crusading, but she is pleased when people say they are touched by it and is thrilled when teachers use her as an example for children who are going through a tough time. "I would love this story to reach people, especially young people in the situation I was in," she says. "I had no model for this story. I was studying African American women's writing and that wasn't a model, and Virginia Woolf certainly wasn't. I felt in need of a tradition to write in."

Her mother, who comes across in the book as deeply flawed, gave her nothing but encouragement, Andrea says. The chapters in Granta came as a shock because she apparently had not known about the time Andrea's first stepfather knocked her out or about his sinister sexual threats. But she insisted that her daughter write the book in her own way. Now living with a new, non-violent partner in the south of England, she has "retired from the melodrama", Andrea says. "My mother's attitude is that she made huge mistakes that had dire repercussions. She isn't squeamish about those things being depicted."

Neither of her stepfathers is still on the scene, but she is nervous about their reactions to the book should they come across it. "I don't want to be stalked or sorted out, and they both have habits of doing that kind of thing," she says. Her middle sister, Laurie, was at first very shy of being written about. But, Andrea says, she began carrying the first two chapters with her "like a baby - it was her testimony, too". Their younger stepsister, Sarah, found the book funny. This is not as strange as it sounds. "I wrote it in a buoyant spirit with what I hope is a lot of humour and something that would convey the elasticity of children," Andrea says.

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Her sisters have proved to be survivors, too. Having studied languages at Cambridge, Laurie is now in Africa with her fiance and dancing with a number of modern dance troupes. Sarah, who apparently went spectacularly off the rails as a teenager, works in London as a cardiac technician and has a three-year-old daughter. "We all have amazing energy and enthusiasm," Andrea says. "The miracle of surviving fills us. Our mother had strict standards, even if she didn't stick to them. We were brought up to be proper." This was furthered by an extended family of aunties and grannies. Andrea learned early that books were a means of escape, mentally and physically: doing well at school was a way out. "I have a very deep sense of gratitude for having survived," she says.

Despite the trials of her childhood, Andrea still trusts people, but she is wary of circumstances that go well. However, she does not resent people for whom things have always gone well. As an undergraduate she had friends who felt guilty because of their privileged backgrounds and did not want to accept money from their parents. Andrea found that hard to understand: she knew that her mum would have given her money if she had had it. "Children ought to be privileged," she says.

Nor did she find Oxford as a place to study strange. "I had come from minus thousands, so it was always going to be different," she says. She came to it thirsty for books, having read only a handful of works of literature, mainly her A-level set books. In her house, the only book had been a battered dictionary used for crosswords, although her mother had taught her to read at the age of three from Ladybird books. "When I came to Oxford it was abracadabra, " she says. "It was another world. The peace of it was amazing."

She has been in Oxford for nearly seven years, first as a junior dean at Hertford, then as junior research fellow at Lincoln, Woolfson and now Jesus. In her present academic work, she looks at women and modernism, concentrating on configurations of self. She is comparing Jean Rees, the subject of her doctoral thesis, with Katherine Mansfield and Virginia Woolf and their reactions to modernism and the metropolis. She is most interested in how women invent themselves through make-up and stories. Her tutor at Hertford, Julia Briggs, was struck by Andrea's choice to write about Rees, an outsider who was treated badly by the men in her life. Briggs suggests there is a theme in English literature of writing providing women with a lifeline.

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Andrea has already started on her second book. Drawing on her experiences in the US, it will examine the relationship between an 80-year-old blind artist and an 18-year-old girl. "It is the greatest luxury just to be able to make it all up," says Andrea. "Before I was tethered to the truth. Now I'm no longer tethered, at least not to that kind of truth."

Even so, she admits that Laurie and Sarah have a point when they accuse her of toning down their family story. "I left out a lot of things," she says. "I was mostly thinking of my mum, but it was also artistic discretion. A narrative cannot stick that much grisly stuff. Domestic abuse is repetitive, and that doesn't make for a good tale." Thanking me profusely for coming, she puts down her caffe latte and prepares to get back to her timbered study in the centre of Oxford, where the photographer is waiting - one of a long line since her book was published. "My sisters say the book is too tame, that it beautifies what happened. But that's what stories do."

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Once in a House on Fire is published by Picador, Pounds 14.99.