A cop goes undercover to investigate the murder of a woman on New York's Fire Island: "A good yarn populated with well-drawn characters" (Booklist).   Alison, a young, single Manhattan retail buyer, first met Linda seven years ago, when both answered the same classified ad for a Fire Island share. Since then, they've been returning to Seaside Harbor every summer weekend.   But one night, after leaving Crane's, a famed singles bar, Linda is found murdered, and Alison starts to realize how little she really knows about her housemate. Is the killer a spurned suitor? What about the mysterious lover back in the city Linda had spoken of--but whom Alison has never met?   Meanwhile, Long Island police officer Joe DiGregorio has been assigned to work undercover on the case, posing as a yuppie accountant. Together, Joe and Alison--who is unaware of Joe's real identity--are about to unravel Linda's many secrets . . .   "With refreshing insight, Margolis conveys the intensity and the crass materialism that are the hallmarks of a certain breed of young professionals." --Publishers Weekly