Readers of ''High Fidelity'' will remember that Hornby wrapped up that sharp tale of modern love with a disingenuously bright bow of a last scene. Here, the pattern's reversed, and 305 pages of treacle (cut, it must be said, with acid humor) build to a final paragraph bearing more truth about marriage and family than all that preceded it.

"How to Be Good" is partly a wry marital comedy about how a spouse's change of heart invariably destabilizes his longtime partner's own identity, but it's also a thorny parable about the dangers of complacent, conventional self-satisfaction. It's also a very funny and shrewd novel, like Hornby's others, full of acerbic observations about book-buying habits, the virtues of friends who don't really listen to what you say, the tactlessness of children, movies that all seem to "involve spacecraft or insects or noise" and the poisonous bitchiness of those dissatisfied souls who hover in the margins of the creative life.

A generation ago, Western society held an informal plebiscite to decide whether the common good would be better served by sane, decent people like Katie or lollapaloozas like GoodNews. The holy fools lost, and the vote wasn't close. It's anyone's guess why Hornby felt it was time for a recount.

You might say that, by the end, the questions this engaging book opens are too big for the lives it describes; but then, as Katie concludes, aren't they always?

Hornby's prose is artful and effortless, his spiky wit as razored as a number-two cut. There are some delightful comic set-ups, and his dialogue sings with empathy for the discordant voices of ordinary, struggling humanity