For her launch party, Lucy Ellmann wears a Monroe-like red-ruched dress, all curves and cleavage. She looks wonderful: a golden-haired mermaid with sea-green eyes, basking in the approbation of the sleek black seals of London's literati. Very different from Eloise, the self-effacing heroine/hermit of her third novel, Man Or Mango?, who is terrified of any form of contact with people.

How wrong can you be. The dress, it turns out, was pure bravado. When we meet a few days later she's wearing don't-notice-me black, her voice is hesitant and barely discernible above the clatter of hotel staff preparing for lunch. Lucy Ellmann, just like Eloise, is a fish out of water. She has been pathologically shy ever since she can remember but "it was only in adulthood, that I got the chance to explore shyness in a big way. Until then you're forced to go to school. My father always wanted me to have more friends. I didn't find it so easy."

Her father was Richard Ellmann, academic and biographer of Joyce and Wilde. Her mother was Mary Ellmann, nee Donaghue, another English literature scholar whose subject was Tennyson and who "wrote a great book about how women writers are treated differently from men. A very early feminist book which has been copied by a lot of lesser people". Her mother also wrote a novel which she has never read because no one can find it. ("My father always said it was good. And she sent it to one publisher who didn't want it. And that was that for her.")

Although she read Thinking About Women, published in 1969, she has only read bits of her father's work, and he never read hers. He died of motor neurone disease ten years ago, before her first novel, Sweet Desserts was published. A year later her mother died. She had been an invalid for 20 years, having suffered "an aneurysm in the brain - a sort of stroke". From then on Mary Ellmann "participated" but could never be an ordinary mother. "He tended her very kindly for years. Then she got breast cancer. Then he got ill. Then he managed, to all of our surprise and agony, to die first. And then her cancer took over and she died." Now Ellmann worries that she will fail her own daughter Emily, now 14, because she has no experience of what a "nice, active" mother does. "I feel scared that it might not happen. It feels almost like pretending that I can do these things."

Richard Ellmann's move from Illinois to an Oxford professorship came in 1970 when Lucy was 13. Not a good time. And she determined not to go quietly. She hated her new school, clinging like a limpet to her American accent and vocabulary. "I was determined not to become English. I hated having to come so much. It took about 20 years to enjoy being here." Overshadowed by her two outgoing older siblings, the displaced teenager sank into depression and eating disorders, a period that later become the source material for her first novel. She continues to resent the way women are forced to think thin. "Food is an immediate source of satisfaction. And sex would be, but it's harder to arrange." Man Or Mango? is subtitled A Lament. Eloise is a woman who has given up on humanity. She lives alone in a cottage in Hampshire, where mangoes seem infinitely preferable to men. While lack of penetrative sex obsesses her, lack of love is slowly killing her. She deals with the world from behind a door, filling her time making lists, hierarchies and connections: legitimising her fear of people through freeze-framed moments of the Holocaust ("We bear their shock on our shoulders") through newspaper accounts of the Irish Famine; comparing the human capacity for cold-blooded (and careless) cruelty with the social order of ants and bees.

As a study of the pain and solace of being alone, it is extraordinary. Yet never does Eloise sink into self-pity. Like Ellmann herself, her sense of the absurd bubbles up, an unstoppable geyser, keeping her afloat: pain and pleasure, seamlessly and sensuously mixed. Whatever Lucy Ellmann might say to the contrary, Man or Mango? is clearly autobiographical. The Holocaust and the Famine represent the two strands of her inheritance. Eloise's father is Jewish-American, her mother Irish Catholic. (Mary Ellmann was second-generation Irish, her family probably from Mayo.)

Both real and fictional parents eloped to Paris. (The Ellmann parents met on a blind date: "Their courtship was over his Yeats PhD.") Then there's George, the man Eloise yearns for. The man who confounds her misanthropy. Last year Lucy Ellmann married Todd McEwen, an American writer she met 10 years ago at a writers' retreat in Scotland. Is he her George? ("He's my joy," she counters, pun and truth inseparable.) No. They were just friends when they first met. Not lovers. And, anyway, by the time they were reunited the novel was nearly finished. Like Eloise, Ellmann had spent six years on her own.

Unlike Eloise, she had her daughter to keep her company. ("I've really been kept afloat by her all these years.") It's a condition she describes as hermitage. Although she says she has stopped burrowing now, "I still like it. I think it's a great way of living. I just wish people would leave you alone." The dΘnouement of the novel is set in Connemara, in Rossadilly, a thinly disguised Renvyle, where the Ellmanns used to go on holiday and where, Lucy Ellmann explains, "I had been as a happy child - well not happy, I don't think children are happy." It is the only time she has actively done research for a book. "I thought if I could I find it, it would be kind of magical." Ireland itself continues to haunt her. "The Holocaust is the past, yet the Irish thing is still going on. And it's so sad. And such a dream-laden place. The two things, the sadness and the dreams affect me, I guess."

To Lucy Ellmann Ireland and Yeats are inseparable. "It's the one thing I actually enjoyed my father teaching me. He didn't push it. But I had to study Yeats at university and he helped me out then. He was a great teacher of literature." Her experience of academics generally, however, has not been not good. "They think they know everything. They know what literature is really about. And us poor slugs, who make the stuff for them to mess around with, are pretty consequential. Without them we'd be nothing." That her own parents were different, she says, was probably because both had tried their hand at fiction (her father wrote plays) and failed. Even so, when it came to telling them that she was "going to try to write a novel", she was "embarrassed". Richard Ellmann died before he could read Sweet Desserts - a book that went on to win the Guardian Fiction prize - though her mother did. "She was a little shocked but she took it well. I think she knew that might involved hurting people. Honesty is the only hopeful thing. The only hopeful thing in the world is to keep looking for honesty. I think all the rest is a waste of time."

Lucy Ellmann will read from Man Or Mango? At Waterstones, Dawson Street in Dublin tonight at 6.30 p.m.

Man Or Mango? is published by Headline Review at ú6.99.