An affectionate sendup of those summer enclaves with inviolate social rules--here, that each of the old guard has his or her ""day"" to host a party during the season, and that ""day"" is theirs until death does them part. Which is the problem: three of the ""day"" people (Joyce Crenshaw, Betsy de Chambrun, Harry Metcalf) have been poisoned at parties, and the season is a shambles. Widower Tresh Trowbridge, a white-flannel wearer and slightly impoverished stalwart of this set, turns investigator--with the full enthusiasm of his Manhattan-based son Nicky (who wants dad to move back to town) and Nicky's company's database. Also investigating is local Center Hampton cop Walsley, whose chief got riled up and involved along about murder #3. Admits Walsley: ""Basically, he's like, a dead broad's a dead broad, but a dead man's serious."" Did murder/s result from a party snub, or was it some other summer rite (the annual author's tea, for instance) or summer community concern (waterfront property rights, maybe) that caused it/them? Frankly, the solution's a letdown--dumb, really--but en route to it are some memorable vignettes: Guido di Rimini's bodyguards, who are more beautiful than the beautiful people could hope to be, while they usurp the catering rights at a party to insure nothing inelegant, such as poison, creeps in; Nicky's falling hard for the sexual tormentor of his teens, Maud the Bawd; Tresh's carefully worked-out lies to his son to assure him of an afternoon alone with the adorable Flora, his married lover. Logan has a sweet touch with people and is surely the kindliest satirist writing today. Given time, better plotting should come.