LYNN SHARON SCHWARTZ takes a special interest in the interstices of relationships -- in what glues certain people together, where the boundaries between them lie, how they grapple with their differences. Her first novel, Rough Strife, was a mesmerizing study of a marriage. Essentially, it had only two characters: the husband and wife. It was a book as claustrophobic, as convoluted and intense as marriage itself -- a remarkable first novel.

In the second, Balancing Acts, the relationship is one of unrequited love between a 13-year-old schoolgirl and a 74-year-old retired tightrope walker. Alison is chattery, openhearted, breathless, insistent on her "connection" to Max. Max is weary and ironic, often downright rude. He has his mind on more important things: his failing health, his dwindling horizons, his constant grief for the wife who died. While Alison buzzes and twitters around him, Max reflects sadly on his long-gone circus career; he bristles at anyone who reminds him of his mortality; he thinks of how cold his friends must be in their graves. He feels nothing for Alison but impatience, or at best a grudging tolerance. Relationship? You might more aptly call this a hunt, with the hunter growing every more frustrated and the hunted miles ahead, loping along with his nose to the breeze.

There is much to be said for this book. It conveys, movingly, the world of an old man with little left to hope for; it describes a convincing love affair (or perahaps "sexual friendship," if such a term exists) between this old man and his middle-aged neighbor, a marvelously kind and perceptive woman. And at moments, it has an absorbing immediacy, as in this dream Max has of his dead wife, Susie, just when his memory of her seems to be fading:

"He is lying on a bed with Susie, not on any bed they ever lay in together, but the one at home . . . Of course she is gone, dead, he is not deluding himself. But now he has her back. He can feel every inch of her skin through the silky white nightgown. The lights in the room are bright so he can see her clearly too. Though he is next to her, holding her, through the generous magic of the dream he can see all of her, at the same time: she rests in his arms and in his eyes. She sleeps. He knows the dead cannot speak or see. But she feels. She knows he is there. She lies on her side, breathing quietly and steadily, as she always did, with her back to him . . . Her knees are drawn up: the long, bent line of the legs is an L. He can see the contour of her hip bone, under the light nightgown. She is still slim. She has one hand between her knees and one near her face. Her fingers splay out so he can read her palm. But the lines in her palm are all gone. It is a flat unmarked surface. Her mouth is open and the corners of her lips are wet. He pulls her closer."

With her older characters, then, Lynne Sharon Schwartz is successful. But with the child, Alison, I believe she strikes a good many false notes. Alison is too ingenuous, too burbly, too quick to confide her closest secrets to Max. Such children exist, of course, but for the purposes of this story, Alison shouldn't be one of them. She ought to have a little more darkness.

Alison doesn't possess the depth and complexity of the other characters, or of the Rough Strife characters; yet we are asked to take it on faith that she does -- that her Barbie-and Ken-doll parents disappoint her enough so that she will pursue Max for his lack of conventionality; that some undisclosed sense of impotence leads her to yearn for the control and power of Max's acrobatic training. She is described with a certain flippancy that keeps us at a distance; when Max calls her a "pest," we tend to agree, although we're not supposed to. Nothing we see of her quite justifies her intrusiveness. We'd have to be told more, and from further within her, before we could offer the sympathy that the author seems to be trying so obviously to pull from us.

Nonetheless, Balancing Acts proceeds with skill and confidence, and it held my attention to the end. I can easily imagine lending this book to a teen-ager. With the youthfulness of the heroine as the initial hook to draw her into the story, she could learn something important about the needs and sorrows -- the humanity, in fact -- of the elderly.