The Position by Meg Wolitzer

One day, Paul and Roz's children find the book which they have written about their sex life. Called "Pleasuring: One Couple's Journey to Fulfillment", it's illustrated with explicit pencil drawings of every position they have ever tried. The artist has taken a few liberties, but to the children Holly, Michael, Dashiell and Claudia it's obvious that the pictures are of their parents. Later, when Paul and Roz give their children money from the book's vast earnings, Holly describes it as "sex money, I mean, fucking blood money." But she accepts it anyway.

To outsiders, the Mellows seem perfect. They all appear to adore each other and sing chirpy, jaunty rhyming couplets in the car: "Oh we're the Mellows, / Some girls and some fellows. / We're not the Gambles / 'cause we'd be covered with brambles."

They might have sung: "This is a very fine book / With a very good hook. / It could have been greater, / But more of that later."

The Position is too charmed by the neatness of its own choreography. The idea of parents who write a sex manual which is found by their children is clever. But it's too stagily done and Wolitzer didn't manage to convince me that the children's discovery really did turn their lives on a sixpence. "And it did change everything eventually, it did," she argues, almost plaintively.

Thirty years later, when Roz wants to republish a new edition of the sex book (but Paul doesn't), we discover just how much damage has been done. Holly is a recovering drug addict and recluse. Michael is a sexual failure. Dashiell, who is gay, is, horror of horrors for his family, a Republican. Claudia is unconfident and hopeless.

Before the novel ends there's a reshuffling of the pack. Characters reinvent themselves, one becomes dangerously ill, others even pluck victory from the mess they've made of their lives so far. But there's something frustrating about a novel this good which tries to argue that human nature is determined by a single event. Life is more complex, more chaotic and more interesting than that. But Meg Wolitzer is a fine, funny and wise writer. Her emotional understanding is sufficiently acute for me to forgive her that one lapse.