Books: The Last Resort by Alison Lurie Chatto & Windus, pounds 15.99; Queer fish and straight men

When Jenny, the 46-year-old wife of eminent naturalist Wilkie Walker, goes swimming off Key West, she fails to read the notices warning "Danger: Men of War" and is duly attacked by a jellyfish. Far more serious, however, has been her failure to heed the danger posed by Men of Letters. After 25 years of marriage to Wilkie, she finds herself stung.

In a novel pervaded by examples of endangered species, Jenny belongs to the most threatened. She is a "walking anachronism" who "devotes herself full-time to her husband like a Victorian wife". Wilkie is a Desmond Morris figure, a populariser who "had made his point so well that it had become banal". Jenny's contribution to his work goes way beyond conjugal duty, as his books are "full of sentences, and even paragraphs, that she had composed".

Unknown to Jenny, Wilkie suspects that he has bowel cancer and falls into a severe depression. She suggests a trip to Key West and he, considering it a suitable place for suicide, accepts. Once there, his gloom deepens; for, while the climate may be congenial, the clientele are not. It's not so much its position which has earned Key West the title of Last Resort as the haven it offers to people who have nowhere else to go.

The Walkers are exposed to a more varied population than on their New England campus: in particular, Jacko, a gay man with HIV, who is their caretaker, and Lee, the owner of a women's guest house, who rescues Jenny from the jellyfish - and from Wilkie. Lee is particularly hostile to Wilkie's homophobia and his erroneous, as well as irrelevant, declaration that "animals can't be queer". Lurie beautifully handles Lee and Jenny's courtship and the ecstatic liberation of lesbian love ("the air still seemed full of sequinned snowflakes"). The most unexpected facet of the book is its depiction of heterosexual relationships as adulterous and manipulative and homosexual ones as loving and supportive.

Lurie sets up a clear dichotomy between those characters - primarily Wilkie but also Gerry, a self-serving poet, and Myra, a Republican power- broker - who see people in terms of other species (mice, shrews, dolphins, manatees and birds), and those - Lee, Jacko and Molly, an elderly artist - who see them for themselves. Wilkie, as becomes clear to everyone but Jenny, is a monster (if she is a Victorian wife, he is her Casaubon) whose chief concern for her is how she will fare as his literary executor. It is telling that the example she picks of his generosity is his giving "money for the conversion of his books into Braille".

This is a charming, sunny book that seems infused with all the warmth of its setting. Even the air of death and decay that infiltrates in the form of Wilkie's musings on a dying environment, Molly's sense of loss and Jacko's diagnosis, fails to dent the novel's high spirits. It is full of sparkish - indeed, Muriel Sparkish - observations and gently subversive wit. Above all, Lurie exposes the dishonesty of people who wish to protect nature's diversity while demanding human homogeneity. The whole weight of the book lies behind Lee's declaration that "anyone has the right to be in love. It's just a dumb convention that they have to be the same age and race and religion and class, and they can't be the same sex."