This quite aggressively fey little book is described as Nancy Willard's first novel for adults, but only those with severe cases of arrested adolescence are likely to derive much pleasure or satisfaction from it. "Things Invisible to See" is redeemed in part by the presence of one wholly enchanting character, but lovable though this person may be, she does not cancel out the book's calculated whimsy or its pervasive air of silliness.

Willard has distinguished herself as the author of books for children -- she won a Newbery Medal for "A Visit to William Blake's Inn: Poems for Innocent and Experienced Travelers" -- and a children's book is what she has written in "Things Invisible to See." Its principal characters are either children or childish, its plot is characterized by a fancifulness with which children are more comfortable than adults, and its mixture of the actual and the fantastic borrows heavily from the fairy tale tradition. Readers who are able to suspend both disbelief and maturity may well have a good time with it; those who cannot are going to have problems.

The story centers upon twin 18-year-old brothers, Ben and Willie Harkissian, who live in Ann Arbor, Mich., in the fall of 1941. They are a study in contrasts: Ben is outgoing, confident, athletic, while Willie is withdrawn, studious, shy. Ben is waiting for his number to come up in the draft; Willie, with flat feet, is exempt from the service. Ben has a steady girlfriend, Marsha, whose mother has recently remarried into money; Willie has no girlfriend, but tries to enhance his eligibility by boning up on books of etiquette and proper phraseology.

The event that changes their lives occurs one October night when Ben, goaded by a friend, clouts a baseball across a river into a quiet park: "In the darkness under the willows a girl cried out. People strolling along the river on the last warm evening of autumn stopped in their tracks, chilled." The girl, Ben soon learns, is named Clare Bishop, she is 17 years old, and she is paralyzed from the waist down -- though it is unclear whether her inability to walk is caused by the beaning or by other, unknown influences.

Ben does not identify himself as the fellow who hit the ball, but guilt draws him to the hospital. He fabricates an excuse for visiting Clare's room, where the predictable happens: The two fall in love. On Ben's part at least this is entirely understandable, for Clare is about as chipper and winsome a girl as any boy could hope to meet. There's no moaning and groaning for her. "My life isn't wrecked," she says, "I'm going to study at home," and when Ben finally confesses (by mail), she replies:

"What matters is this. If you hadn't hit that ball, we'd never have met. And I think my real life started from that moment. Oh, I ate and slept and walked around, but I was asleep. When I think about my life B.B. before Ben , the days are all the same color, they run into each other like water. There's so much that slipped over me, so much I didn't notice or remember."

Clare is a terrific person, and the novel is at its most appealing when she is the center of attention. But there's more to the story than her, and as is so often the case, more turns out to be less. The Japanese bomb Pearl Harbor and Ben, no longer content to wait for his number, volunteers for the service. He is posted to a lonely island in the Pacific, then is blown to sea in a severe storm. The moment of his death is at hand when Death himself appears and offers a bargain: Death and his baseball team will play a game against Ben's old team, the South Avenue Rovers, with death or life resting on the outcome.

Death, of course, stacks the deck by loading his team with immortals long since gone to their graves, and other complications ensue that cause great uncertainty about Ben's fate, but by this point only the most tolerant reader is likely to care. The moment the story no longer is earthbound, its plausibility completely vanishes; Willard simply can't pull off the mixture of fact and fantasy -- Gabriel Garcia Marquez she most certainly is not -- and at the end the novel dissolves into an amiable but pointless puddle.

Willard is a capable writer, and Clare Bishop is evidence enough that she can create an appealing, convincing character. But "Things Invisible to See" is too cute by half, and its eagerness to please quickly becomes cloying.