An unhappy teenage girl's obsession with an unhappy rock star--in a thin, modestly talented first novel that begins promisingly, then pretty much falls apart. The book's first, far better half is the Spring 1975 diary of Los Angeles high-school senior Susan Daniels, who broods--but not too goopily--over the recent suicide of her frail, odd, 14-year-old sister Effie: Susan recalls the devastating breakup of their parents' marriage (when Effie was eleven); she remembers how Effie's subsequent depression lifted as she became obsessed with rock star David Angel (starting a fan club, even traveling around the country to concerts); and she recounts how Effie mysteriously disappeared one day (just after Dad announced a forthcoming new wife), then returned, heard the news that David Angel had shot himself, and did likewise . . . with a note saying that life without Angel was ""too empty."" Susan isn't satisfied, however--""There must have been more . . . a real reason""--and indeed the whole diary is nicely shadowed with lifelike gaps, along with enough convincing, mundane details to maintain a quietly compelling measure of credibility. But then, unfortunately, Sheldon provides the solution to the mystery: a limp tidbit of melodrama which is only revealed after a spotty pastiche covering the drugs-and-loneliness life of David Angel himself. There are fragments of posthumous testimony about poor David (real name Joey Danzig) from friends, lovers, and a selfish ex-wife. There are a few maudlin scenes of David/Joey padding unhappily around his mansion, leading up to the day of Effie's mysterious disappearance, when she in fact visited David Angel . . . who tried to rape her (confusing her in his mind with a long-lost love). But, psychologically, none of this is very persuasive. And, unlike more skillful scenarios which use multiple viewpoints to create suspense (e.g., Sebastien Japrisot's One Deadly Summer), the effect here is that of a mildly absorbing riddle followed by undeveloped scraps from some other story and an artificially delayed punchline. Still, the first half is gently involving--with strongest appeal to YA readers--and the book is short enough to make waiting around for that denouement fairly painless.