Diana Evans's publishers are hailing her as "the new literary voice of multicultural Britain", and compare this edgy debut with Zadie Smith's White Teeth and Monica Ali's Brick Lane. In fact, it has little in common with either. 26a is a novel of personal rather than cultural alienation, concerned less with questions of racial identity than with the struggle to forge a link between what Katherine Mansfield called "the secret self" and the shared, external world. The novel is saturated with disorientation and exile, but its underlying sense of unbelonging is, for Evans's characters, simply "the colour of life". Late 20th-century Neasden is as bewildering for Aubrey Hunter, who escaped to London from middle-class Derbyshire, as it is for his wife Ida, who grew up in Nigeria. The "new country" that this unlikely couple inhabit is their unsatisfactory marriage.

Mr and Mrs Hunter live their emotionally slim lives at 26 Waifer Avenue with four daughters, two of whom, Georgia and Bessi, are identical twins. This pair mostly hole up in the sanctuary of an attic bedroom that they have named 26a. Here, they discuss the world and their self-referential place in it - disturbed, as the novel begins, by little except mealtimes, the seasons and the smell of Vicks. Georgia is quickly established as the novel's centre of consciousness. Her voice is rich with the intensity of childhood as she relates the main events of "The First Bit" of her story, when the twins share almost everything.

Midway through the novel's first section, Aubrey Hunter's job with Alders Financial takes his family to Lagos. They stay for three years, in "thermal" heat, with "sunny swollen rainbows waiting in the wings". The children have cartwheel olympics, the grown-ups have parties. Gin is consumed, Val Doonican danced to, and Georgia's brooding sense of difference is given focus in the fumbled rape she endures at the hands of a family servant. This potentially schematic turning point is subtly worked. Georgia's voice becomes not mawkish but absorbingly trance-like, without "the now-ness of things" to connect her to Bessi, whose robust adolescent adventures she attempts to share but cannot enjoy.

Back in Neasden, Georgia becomes clumsy - literally losing her grip on whatever she holds - in a world that seems "no longer solid". She notes her family's bubbling dysfunction in increasingly fluid sentences, which describe an in-creasingly liquid world. It rains a lot, her mother takes long baths and her father takes to drink. The eldest sister gets pregnant, the Derbyshire grandmother is hit by a car, the twins are put into different forms at school.

All this physical trauma is blended into a lyrical mix of emotional collapse. Aubrey Hunter's reaction to his mother's amnesia after her accident is "a lost feeling, like a teenager who had left home for the first time". Georgia feels "halved and doubled at the same time" without Bessi beside her in class. "It was foreign living like this . . . the way the others did . . . the twinless ones."

By the end of her crowded but lonely story, Georgia is hopelessly lost. A romance with an endearing drifter, a place at Middlesex University and weekly therapy sessions fail to undermine her suicidal state. Evans, too, seems somewhat lost in the final section of her novel, which is perhaps inevitable, given her decision to chart Georgia's depression as minutely as she does, and to continue the narrative into Bessi's attempts to come to terms with the loss of her twin. The book's conclusion is ragged, which is disappointing but not fatal. At its best, this is a poetic, complex and lingering study of forces that can make life sometimes unliveable, wherever you come from, and wherever you live.