`I was born here in Dublin. It's funny, this is the first time I've ever been able to say `I was born here'." Shani Mootoo, a 41-year-old Trinidadian of Indian extraction, is sitting in a Dublin hotel, blinking. This is the first time she has returned to Dublin since she was three months old.

Here to promote her first novel, Cereus Blooms at Night, she is determined to revisit Holles Street, scene of her birth: "Does it still exist?" She is delighted to hear it does. Mootoo's parents came to Dublin because her father was studying medicine at the Royal College of Surgeons. Her parents stayed in Dublin while she returned to Trinidad to live with her grandparents. She has a compelling memory from her childhood, which was scarred by years of sexual abuse: "When I was six years old and going to school, huge periwinkle snails used to come out after the rain. Boys would stomp on them. Because of my own private situation, I could empathise with those snails." Out of this memory grew the germ of Cereus Blooms at Night, a powerful tale of suffering, retribution and rehabilitation akin to Toni Morrison's Beloved.

Mala Ramchandin, the central character, who is sexually abused by her father, has an affinity with snails: "For Mala, snails and the natural world she connects with are far more benevolent than the sort of danger she encounters from human beings. Nature is never hateful, but human beings are." Set in the town of Paradise on the island of Lantanacamara (a fictionalised Trinidad) the title of the novel refers to a beautiful flower with ugly leaves, which blooms there only once a year, at night: "For the last 15 years I've been a Buddhist," says Mootoo, "and the main symbol in the Buddhism I practice is the lotus flower, which only blooms in a muddy swamp."

As the symbolism of the title suggests, survival in the teeth of abuse, abandonment and madness is the theme of the novel: "I'm a survivor of incest and I'm a lesbian, so I know how easy it is - too easy - to remain in the place of the victim," says Mootoo. Instead she continues to practise the habit her grandfather taught her of going out at night to wish on the stars: "Hope led me to survive and not curl up and die."

A major part of her novel is an exploration of the nature of colonialism, as exhibited by the interfering Thoroughlys, a missionary couple who arrive in Lantanacamara from "the Shivering Northern Wetlands" (Great Britain), and take Chandin Ramchandin, a young Indian boy, away from his parents and labouring background to bring him up as a young Christian gentleman: "Throughout the entire book, you are brought back to the Thoroughlys. They are the foundation of a lot of the heartache," explains Mootoo. There are obvious parallels with the effects of colonialism in Ireland in this scene where the Ramchandins' neighbours discuss the advantages of Reverend Thoroughly's mission school: "When we get sick and we have pains, who looking after us? We looking after our own self, because nobody have time for us. Except the Reverend and his mission from the Shivering Northern Wetlands. All he want from us is that we convert to his religion. If I had children, I would convert."

Inevitably, however, the arrival of the Reverend makes Chandin ashamed of his own background. This is evoked in the following passage, which also exhibits Mootoo's striking capacity to describe smells: "His mother, smelling of coals and charred eggplant and a sweat that embarrassed him with its pungency of heated mustard seed, had quickly pulled her orphanie over her head and nose and mouth." Mootoo depicts the way the islanders attempt to unshackle themselves from the paralysing effects of colonialism: "In Trinidad, the legacy of colonialism is everywhere, but under the surface. I see every problem linked with it."

However, she is always wary of simplification and quick to say that colonised people are often the most narrow minded: "People who are marginalised can think they OWN marginalisation. I have thrown all kinds of different characters into the book so that if you sympathise with one person you find yourself inevitably sympathising with another whom initially you might have hated."

Thus we meet Lavinia Thoroughly, the lesbian daughter of the missionaries who runs off with Chandin's wife Sarah; Tyler, the male cross-dressing nurse who looks after Mala in her old age; and Otoh, the girl who has always dressed and acted as a boy. As Otoh's mother Elsie declaims: "You grow up here and you don't realise almost everyone in this place wish they could be somebody or something else?"

When Mootoo was growing up in Trinidad, such desires to "cross the line" were frowned upon. One of the reasons she moved to Vancouver was because she was a lesbian: "I'm not very good at hiding." She has spent most of her adult life as a visual arts practitioner (her video art has appeared at the Venice Biennale and at the Museum of Modern Art in New York).

Her parents didn't like her early writings, which expressed her dawning sexual orientation towards women: "I started off loving writing as a child, but the words I wrote got me into trouble. It made the adults angry and sad. I think that's why I began to paint, because it was a more ambiguous form of expression."

Moving to Canada has given her a vital perspective from which to write about Trinidad: "I needed the permission of distance. Incest and sexual abuse were completely invisible subjects when I was growing up in Trinidad. Homosexuality, especially in women, was an offence."

Cereus Blooms at Night (which was short-listed for several major awards when it was published in Canada in 1996) is full of exotic scents and tastes, and garlanded with extravagant descriptions and metaphors. These are ingredients which nowadays we tend to wrap up under the label of "magic realism". Mootoo believes such categorisation is not only lazy, but inaccurate: "The term `magic realism' grew out of life and death situations in South America. It was a way of talking about things that for political reasons people could not discuss directly. I feel like an upstart to have my book described as `magic realism'."

Nevertheless, Cereus Blooms at Night has its own political message in that it explores the effects of sexual abuse: "A horrid subject that can be more easily addressed using metaphors and exaggerations", she admits. She is specific as to the literary tradition in which she wishes to locate herself: that of the Canadian immigrant writer. Other examples are Michael Ondaatje (whose work she greatly admires), Rohinton Mistry and Larissa Lai: "They include a mythical fictitious place - an entire other life, a former sensibility - in their description of the Canadian landscape."

She is "pleasantly shocked" that her book, originally published by Press Gang, a small Canadian press, has gone "mainstream". The only down side of her success is the criticism she has received from lesbian writers, who are dissatisfied with her rendition of the relationship between Lavinia Thoroughly and Mala's mother Sarah (Sarah abandons her children to elope with Lavinia). "They want me to fulfil their agenda. But if I enter a book with an agenda, it flops. It's didactic and unpleasant." And "didactic" and "unpleasant" are two words which could never be applied to this impressive, multi-faceted, compassionate first novel.

Cereus Blooms at Night is published by Granta at £14.99 in UK