Dinner With Friends, Hampstead, London

Unrestrained appetites

Friends, it's been said, are God's apology for relations. But what happens, as the American writer Donald Margulies asks, when one's surrogate family start behaving as badly as one's own siblings or parents? Unlike relatives, they have been chosen by us, so they seem not only unpleasant but treacherous. Like spouses.

Dinner With Friends starts like a conventional quasi-comedy – Gabe and Karen, a Connecticut food writer and his wife are ecstatically re-living every minute of their visit to a famous cook in Italy ("The pomodoro! Tell her about the pomodoro!''). Beth, their friend, bursts into tears and reveals that Tom, her absent husband, was not suddenly called away on business but has left her for another woman. Gabe is stupefied, Karen incensed.

They offer dessert, which Gabe proudly calls "limone-mandorle–polenta'' (Beth speaks no Italian), and Karen rushes in with more manageable anxieties ("You don't think I could've beaten the eggs a little bit longer? Don't you think it could've been a little fluffier?''). All eat in silence.

At this point you might think you know where Dinner With Friends is going, but you would be wrong. Karen and Gabe's sensual and analytical preoccupation with food is not a means of evading or compensating for their unhappiness with each other. The mild-mannered Gabe is neither squashed by brittle, picky, pouncing Karen ("I am not 'strict'. I resent that... I'm principled''), nor envious of his sexy friend. Indeed, the more he hears about Tom's catting around, the more he is repelled by it – even though he learns that Beth is not the victim she makes out.

After Who's Afraid of Virginia Woolf?, where does a writer of a two-couple play about troubled marriages go? Donald Margulies provides a satisfying answer in this rueful, edgy but genteel (in the good sense) play about divorce, Connecticut-style, smartly directed by Simon Curtis. Elizabeth McGovern is very funny as a bohemian cutie-pie whose lawyer husband has not only flown the coop but, even more humiliatingly, done so with, she says, a stewardess. (Her husband keeps protesting, "She's a travel agent!'') Rolf Saxon and Samantha Bond also shine as their foodie friends, who try to balance fairness and loyalty. The mixture of emotions and revelations is as affecting as it is unexpected.

To 28 July (020-7722 9301)