What happens when adultery threatens a longtime ""perfect"" marriage? Forster (The Bride of Lowther Fell, Georgy Girl) gives that rather tired premise a relatively crisp, very British run-through--with enough ironic touches and enough variety of viewpoint to keep this short novel moving along, always just above soap-opera level. Pleasant, unaffected Anna has been cozily married to handsome London publisher Robert Osgood for 20 years: three kids, a country cottage, sex still good (if not frequent). So what'll Anna do when Robert, a rather childish sort, writes her a letter confessing to a love (not-just-sex) affair with ambitious young copy-editor Claire? She pretends that she never got the letter, that's what; she even tries to trick Robert (via devoted secretary Betty) into believing that the letter never got mailed. Meanwhile, however, Anna does confront no-nonsense mistress Claire (who says ""I think it's up to you to sort him out, don't you?""). Meanwhile, too, distraught Robert confesses to eldest daughter Sarah--a promiscuous, slightly horrid 18-year-old who reacts first with cool matter-of-factness, then with increasing old-fashioned-ness. And through it all, even over a cottage weekend, Anna and Robert can't bring themselves to any direct discussion of the crisis. Only when Anna at last breaks down and takes herself off to a hotel for two days does the wrangle reach something like catharsis: Robert finally breaks with Claire (who has a good cry, then decides to find ""a normal married man"" next time); and the marriage survives--though the Osgoods have lost their innocence, now knowing that ""all marriages need luck as well as love. . . ."" Forster never cuts very deep in this domestic scenario, leaving the principal characters (especially English-husband-type Robert) blandly sketched-in: only secretary Betty, a sort of Georgy Girl spin-off, comes across with vivid particularity. Nor do the communication mixups ever rise to genuine comedy. But, with a slippery, unsentimental focus (which also takes in the Osgoods' cleaning lady and Anna's envious/catty girlfriends), this tempest-in-a-teacup becomes a mostly agreeable, fairly observant case-history.