At her best (The Best of Everything, Class Reunion) Jaffe hits home with shrewd, if superficial, character studies; but this time her glossily appealing people are tied to an ill-conceived melodrama that mounts in implausibility as it lurches from group obsession to schizophrenia. The focus is on four undergraduates at Grant U. in Pennsylvania--all of them bright and attractive but each with some hangup in his or her upper-middle-class background: beautiful Kate has divorced California parents and a sexy new stepmother; Travolta lookalike Daniel (a campus super-stud) is pushed toward perfection by his intellectual-Jewish parents; impish Jay Jay is essentially neglected by his divorced, super-achieving N.Y. parents (a publisher, a decorator); and handsome Robbie is haunted (like his alcoholic mother) by a teenage brother who ran away from home, never to return. Presumably because of these rough realities, then, the four friends (Kate and Robbie are soon lovers) turn to fantasy, obsessively playing a game called ""Mazes and Monsters,"" in which they imagine themselves to be Tolkien-esque heroes facing life-and-death perils. But Jaffe never succeeds in making this obsession (or the boring game itself) credible; and when Jay Jay insists on making the game real-er--by playing it in some genuinely dangerous caves near the campus--it merely gets sillier, with Kate dressing up in chain-mail as ""Glacia, the Fighter."" In fact, Jaffe herself seems to get bored with the game idea about halfway through. And her attention then shifts to the ludicrously unconvincing onset of Robbie's psychosis: he breaks off the affair with Kate (she quickly finds grand passion with Daniel); he identifies totally with his game character (Pardieu the Holy Man); he disappears to a bum-like existence in Manhattan, nearly kills a man who mistakes him for a gay hustler, and is finally found and protected by his friends (who have now, patly, come to face reality). Dubious psychopathology, sketchy family problems, YA-style (each set of parents gets a couple of flashback pages), haywire plotting--but Jaffe's smoothly readable prose and soothingly affluent backgrounds may provide enough diversion for her sizeable following.