Writer seeks 'wife' for year on tropical island."" Irvine, a 25-year-old Britisher, answered that ad in 1981 and did indeed spend a year on the small uninhabited isle of Tuin (in the Torres Strait between Australia and New Guinea)--with Gerald Kingsland, a.k.a. ""G,"" a 50-ish, rough-talking, divorced ex-publisher. Why did Irvine go along, even agreeing to the legal marriage demanded by Australian authorities? Well, despite some woozy prose about ""the element of the unknown,"" her motives and character remain unclear here, with virtually nothing of her pre-island background: an increasing problem through this intriguing, uneven memoir. Still, when sticking to the gritty details of life on Tuin, Irvine is a talented, vivid diarist. Dropped off on the island with minimal supplies, Lu and G have to depend on fishing and coconut-gathering for food. (Among the recipes: ""Barracuda Vinaigrette."") Fresh water is scarce; strict rationing is imperative; wood-chopping is a daily necessity. The couple's personalities clash: ""My jolly-hockey-sticks Sergeant-Majorishness was anathema to G. His lackadaisical attitude to getting our everyday life organised on Tuin appalled me."" G suffers from insect-bites, crippling leg ulcers; Lu eats poisonous beans; there's dreadful drought, severe weight loss. But then neighboring Islanders start visiting--bringing food, seeking G's help in fixing machines, inviting the couple to native festivities. (""We were to be adopted."") And though this contact results in regained health, charming encounters, and G's emergence from sour depression, it's a distinctly mixed blessing for Lu--whose mystical attachment to solitary Tuin has thus been compromised, with loss of identity and ""the dissolution of my character."" This island-passion (""I was more possessive of Tuin than I had ever been of any man"") is less than completely persuasive. Even more tenuous is Irvine's chronicle of her problematic conjugal life with G: though there was pre-marital sex, she didn't ""fancy"" G and rejected his constant island advances; G felt ""justified resentment""; and, in the last three months, Irvine grudgingly changed her policy--resulting in G's devoted delight and her own rueful, knotty ambivalence. . . before departing with both relief and regret. (""As a cunt""--G's perennial epithet--""I was beginning to feel almost professional."") As the record of an unusual relationship, then, this is sketchy, a little pretentious, and faintly off-putting--though not without a certain coy/super-sex-woman appeal. (First serial rights to Cosmopolitan.) As an island chronicle, however, part-survival and part-anthropology, it's bright, precise, and often amusing.