In her debut as a novelist, Caroline Leavitt draws the reader into the world of a Nelson family which no one could mistake for that of Ozzie and Harriet. Told in the first person by Bess Nelson -- daughter of Bea and Ben, sister of Rozzy -- "Meeting Rozzy Halfway" is a sitcom viewed not on a television screen but through a cracked bell jar. The elements of humor are there: the health-faddist, lawyer father; the attractive mother who tries to maintain harmony; the wacky oldest girl; the younger one, more conventional, caught between loyalties.

But it's not funny.

Rozzy, you see, has problems. She's not just lovably wacky; there is a name for what she has. Beginning in her 5th-grade year, Rozzy Nelson exhibits the behavior of what looks most like a "process" schizophrenic. Those suffering from this disorder manifest it gradually in such ways as inappropriate social behavior, inability to make friendships and, most particularly, bizarre habits.

For example, Rozzy is found in a puddle of her own urine on the floor of the school laboratory; she talks "to herself, slapping at imaginary birds flying around her, pecking in her hair for bread crumbs"; she wears herself out, frantically galloping like a horse. A birthday for Rozzy must be called off when half the schoolgirl guests nervously make excuses and cancel.

There are other symptoms of schizophrenia -- limited emotional response, detachment from reality, periods of extreme excitement -- and eventually Rozzy, in her "bright darkness," flashes the whole array. How does the Nelson family cope? For Ben, to whom Rozzy had been a "miraculous" child, his oldest daughter's actions are reprehensible, a betrayal of the loving adoration he has previously heaped upon her. As for Bea, "Ben never blamed Bea, no more than he blamed himself. It was always something in Rozzy, in her metabolism, her diet, things that could be controlled."

Bess, certified "normal" by a doctor anxiously consulted in the wake of the distress caused by Rozzy, monitors the situation from an early age. She yearns to have bonds with her sister whom she helplessly loves and sees spinning away from her, cocooned by her aberrance. As always, there is the dangerous allure of madness, its glittering strangeness, and not only Bess but later a lover, Stewey, fall under Rozzy's spell.

By the time they are both in college, with Rozzy more in-and-out than in, Bess' attachment to her sister has endured and strengthened, despite Rozzy's capricious floutings of it. Bea and Ben Nelson, meanwhile, are left behind, as if stranded on an island from which their offspring have shipped out. Ben is hostile while Bea is ceaselessly conciliatory; the years of strain bring to each of them their own forms of deviant behavior.

But the ordeal is not over, not just yet: Rozzy is, as Leavitt portrays her, a natural phenomenon like a meteor which must play out its brilliance across the sky before it burns itself up. That which is directly beneath such a distant object, in this case a family that little realizes how far away their daughter/sister is, can only watch. Then the shadow falls, and the light, flickering out, leaves darkness in its place.

When Leavitt succeeds with her probing into the Nelsons, the book gleams with her own pleasure. Her prose is that of a born list-maker as she catalogues, with cheerful precision, the tick-tick-tickings of each of her characters. Up to a point it all works; at first one is delighted with Leavitt's tidiness and polished paragraphs. As the story wears on, however, as we are thrown more and more into the bosom of the Nelson family, there is a feeling of claustrophobia, of being crowded with detail like a bursting closet.

The charm of Bess' voice, so jauntily reportorial (and so marvelous when she talks of her mother's first romance before meeting Ben, an episode that fits oddly into the structure of the book) in the beginning, begins to wear thin. It even starts to seem a bit precious, and when that happens the whole carefully layered structure wobbles.

But I'm not sure if Leavitt should be praised or blamed for these effects her style produces. Perhaps she has created a style which corresponds to the nature of the fiction she has invented. Perhaps her light touch is meant to seem heavy as the novel progresses, as Rozzy's moods dominate and her own buoyancy begins to drag her down.

Like Judith Guest's "Ordinary People," "Meeting Rozzy Halfway" shows us the dark side of upper-middle-class American family life. Here the setting is the suburbs of Boston, not Chicago; here there are two daughters, not two sons. But underlying both of these stories is the same desire to get at the heart of what happens between siblings and also between parents and to decode the complex messages exchanged within the family organism. The symbiotic relationship between Bess and Rozzy -- who is Beauty? who is the Beast? -- emerges as Leavitt's final point, but she has made other more important ones along the way.