Can you make an adult novel out of four pretty, happy, rich, smart, rather sweet, and thoroughly two-dimensional Manhattan characters? The answer is yes, sort of, if you adopt the knowing, slightly smug comic tone that one finds in New Yorker cartoon captions. Colwin, whose previous fiction (Shine On, Bright and Dangerous Object) juggled stylistic sophistication with women's-magazine sentimentality, here abandons the heart-on-sleeve for the tongue-in-chic, setting off echoes--some engaging, some just coy--of such disparate romance-watchers as Dorothy Parker, Hollywood in the Thirties, and, most disarmingly, P. G. Wodehouse. She alternates between two romances--the happy marriage of Guido and Holly and the pseudo-harrowing courtship of Misty Berkowitz by Vincent Cardworthy (Guido's cousin). These folks have what you'd have to call minor-league problems. Very romantic Guido (who oversees the family arts foundation) has to learn to accept that picture-perfect Holly sometimes needs to go off and be alone; she's afraid of getting too used to everything being so wonderful. Even more romantic Vincent (who is the Board of Planning's expert on garbage) has to cut through language-expert Misty's Jew-among-Gentiles hang-up and her anti-romantic, serf-protective (and rather tedious) snarlings. Through most of the problematic festivities--Misty's jealousy, Holly's pregnancy--it's a pleasurable relief to find the business of contemporary relationships being tossed around so blithely and reaching such cheerful resolutions. And there are a slew of funny lines (""Friendship is not possible between two women one of whom is very well dressed"") and near-cartoon supporting players to juice things up. But eventually we don't feel that the theme (""Our trouble is that we don't know how things are supposed to be any more"") has been dealt with--or, more important, that we really know any of these ultimately somewhat annoying people. Capable of such a telling line as ""the bedroom looked like a bedroom in a consoling children's story,"" Colwin surely will produce a story that stays in the mind; this edgy, expert entertainment seems to be trying to leave something behind, but it all rolls merrily right by without a trace.