Attachment, by Isabel Fonseca

Howls and kisses on an island of lost love

The plot in Isabel Fonseca's debut novel strikes out in fine arresting form but quickly dissipates and doesn't stand up well, even after the twists and turns of its revelatory ending. It's almost as if a plot has been tacked on to a melancholy musing on human frailty, and the mortal sadness of ageing.

The 45-year-old American Jean has been married for 23 years to Mark. Both highly successful media professionals, they live on the fictional island of St Jacques, a Frenchified paradise in the Indian Ocean, while maintaining a house in Camden Town looked after by their student daughter, Victoria. One morning, Jean opens a letter addressed to Mark and discovers a gushing slice of erotica, clearly part of an ongoing affair, directing him to his e-mail "pleasure address".

She fails to confront Mark directly (she's dashing off for a mammogram appointment, he's in the loo) and later opens the e-mail in the island's internet café, only to be confronted with a series of crass porn shots of the letter writer, 26-year-old, big-breasted Giovana. On an impulse she types a reply in the style of a slathering dirty-old-man Mark, and presses the button. Thus begins a prolonged erotic correspondence that becomes an addiction.

Other blows follow: the mammogram is dubious, Jean's well-loved father in America falls seriously ill, and so Victoria's flight from the nest takes place almost behind her back. Impelled into her own "Olympic dive into the porno pool", Jean finds herself involved in an ill-advised and drunken one-night stand, rediscovering the intensity of hungry kissing, while noting that the man is a bit of a creep. What she is chasing is the feeling of being fiercely alive, a small bulwark against the sea of uncertainty stretching before her. Open moleh, as the islanders call it, "life sadness": the moleh being the fontanel.

Fonseca writes best when skilfully evoking interior states. Jean "grasped within herself a change that was basic, mineral, beyond the realm of mere disappointment". She contemplates the post from England: "the latest batch of expired announcements and last-chance offers seemed to prove that, if you waited long enough, nothing mattered." Not an emotionally involving book, Attachment is often sensitive, and carefully observed. Watching the hairy hands of the male technician positioning her breast like a lump of dough, Jean reflects that the real reason younger women don't get mammograms is that "their breasts couldn't yet swing out onto the tray."

Changes in the body are mirrored in the changing nature of marriage, "with all its unrelieved specificity unfurling over the years". Still not confronting Mark, Jean pictures his love-making with Giovana, comparing it with married sex: "When she and Mark made love it was like a silent movie, with some happy and winded joint sighing at the end". With Giovana, she imagines his newfound range, "from Gregorian chant to the howl of an unanesthetized amputee".

Though the action moves to London and New York and takes in two or three sub-plots and several characters, what's important is the character of Jean, a besotted incomer knowing she can never truly belong, and the vividly realised island of St Jacques – beautiful, seedy, surreal, exotic and impoverished. That's what's memorable; with the gear changes of a long marriage, and the clear demonstration that hungry kisses and howls don't equal love.

Carol Birch's latest novel is 'Scapegallows' (Virago)