Ordinary People : THE BOY WHO WENT AWAY.<i> By Eli Gottlieb</i> .<i> St. Martin’s Press: 224 pp., $21.95</i>

For Denny Graubart, the protagonist of Eli Gottlieb’s accomplished first novel, the summer of 1967 is a confusing time. His beloved Yankees are plummeting in the standings, the carnage of Vietnam is on display on TV and Denny is standing on the cusp of adolescence, a time when he is filled “with the beginnings of something.”

But Denny’s is not an ordinary adolescence. His mother, Harta, has taken to wearing lipstick and short skirts and to disappearing at odd hours of the day. People who shouldn’t know her seem to know her well--postmen, delivery boys, grocers, doctors. She may be having an affair, perhaps several. As Denny’s friend Derwent says, “You know those supersonic dog whistles? It’s like your mom has one in her body. Guys can sense it.”

Meanwhile, Denny’s father, Max, has retreated to the basement, “trailing a yeasty fog of alcohol.” And Fad, Denny’s brother, suffers from autism. Fad rocks back and forth and bites his hand until it bleeds. His speech consists of a string of non sequiturs: “Why when I touch the grass is it like eating soup in my head?” “When I’m dead,” he asks Harta, “can I have some cotton candy?”

On some level, Fad’s illness is what glues the family together, even as it tears them apart. For in the wake of stricter laws about mental illness, Harta must fight to keep Fad out of an institution. She takes him to a series of doctors and spends the summer “role-playing, with him, trying to teach him how to behave in public--how to order food in a restaurant, how to call the police, how to brush his teeth, how to comb his hair.”

Denny, in turn, is neglected. He imagines carrying a sign with him, an advertisement for himself: “This Boy Is Only Incidentally Related to . . . the Tall Gawky [Boy] Who Is Jumping Up and Down . . . . He Has a Good Side-Arm Curveball and Corresponds With At Least Two Learned Societies. Talk To Him, Get to Know Him, Enjoy the Surprising Pleasure of His Company.”

Part of Denny’s confusion comes from simply being an adolescent, from the sense that “adults [are] a race apart, grown up in another country and speaking our language only by a freak accident of human science.” Or, as Derwent puts it, “Two people you never even met before get drunk one night and ball--and that means you have to spend the next 18 years walking around in hand-me-down pants, mumbling ‘Bless this food our daily bread’? “

But the real difficulty Denny faces is that his parents deny anything unusual is taking place. “We’re just like everybody else,” Harta tells Denny. “People walking down the street arm in arm have trouble with their grandparents, honey, who are locked in their rooms upstairs and fed with snorkels.” Fad, according to Harta, is “not retarded, but underutilized.” Even Sabina, the girl Denny has a crush on, thinks Denny is crazy. His mother, Sabina tells him, isn’t having an affair. “Maybe you need something to do with your time,” Sabina says. “Have you thought about a paper route?”

In response to these denials, Denny becomes a spy. He snoops around his parents’ house, he makes a log of everyone’s phone calls, he purchases a fingerprint kit and keeps track of what medicines his parents are taking, he steams open envelopes, he even drills a hole through the wall in his closet so he can spy on his family unobserved.

Denny’s spying, of course, serves as a metaphor for his estrangement. But it does more than that. It’s his way of coping with his confusion, which is both amorphous and all-encompassing. He looks everywhere for signs, though he doesn’t always know what he’s looking for.

Denny is Gottlieb’s most impressive accomplishment. He’s a deeply affecting character, at once precocious and naive, filled with a quirky adolescent sensibility. “Harta served Swanson fried chicken TV dinners, which I loved because they tasted great and allowed me to pretend that we were sitting in an airplane eating dinner while taxiing for takeoff. I made a variety of propeller noises while eating, but nobody seemed to notice.”

Yet Gottlieb doesn’t sentimentalize Denny. Denny may be winsome and humorous, but he’s also cruel. He provokes Fad when the authorities visit, in the hope that they will take Fad away. He physically tortures Fad. He smashes a doll that Sabina has given him. He exacts violent revenge against Harta’s lover. Cruelty gives Denny a certain frisson. “I enjoyed the flavor of being mean,” he says. “It seemed to me a daring, refined thing that was something else besides: a force for truth.”

At times the novel’s architecture shows through too clearly. There are repeated chapter endings: lessons between Harta and Fad turned violent; aborted attempts on Denny’s part to confront one of his parents about his mother’s extra-marital affair. Repetitions aside, Gottlieb’s reliance on drumroll and cliffhanger chapter closings gives the book a slightly herky-jerky feel and reeks a bit of false suspense.

This is a small problem, however, in an otherwise excellent novel. Especially notable is the book’s climax, when Harta’s affair is acknowledged and Fad’s fate resolved. This scene, in the hands of a lesser writer, might easily have descended into melodrama. But Gottlieb handles the material deftly and with a surprise or two that feel just right.

In the end, the book is surprisingly moving. All along, Denny wanted Fad to leave, but when he seems about to get his wish, he feels “a strange lump in [his] throat, almost like a bruise.”

“Denny,” Fad says, “I don’t want to be a boy who goes away.”

Denny isn’t sure he wants this either. He ends up spying again. He finds evidence on his father’s breast pocket of perfume that’s not one of his mother’s brands; maybe another affair is taking place. Even as the book closes, it opens up. Denny senses that something is amiss. His family will always be inscrutable.