A thesis novel is wrecked by the author's sentimentality and by excessive zeal in trying to show that the retarded are almost always better off outside institutions. O'Conner (Stealing Home, 1979; Defending Civilization, 1988) begins well enough by depicting a winning and believable retarded youth, 18-year-old Brendan, who speaks in two- or three-word sentences and likes to be called ``Boombah.'' It is only at the end of the book that the author pulls the rug out from under his creation by revealing, in Brendan's interior monologue, the surprising but unexplained fact that he thinks like a sophisticated, mature man using polysyllabic words and lengthy sentences. The entire novel is narrated in the first person in different voices by 22 separate individuals, all but four of whom are given only one chance to tell their part of the story. The exceptions are Brendan's teacher, Sarah; his widower father, Joseph; his girlfriend, Beatrice; a power-hungry organizational man, Tucker, who wants Brendan for his community house project; and a Runyonesque gang chieftain, Salvatore, who serves as a deus ex machina. In summary, Brendan annoys a high-school principal by hanging around the school, then escapes from a vandalism charge by hanging out with homeless people, is caught and railroaded to a community house that's rife with behavior-modification despotism and numbing drugs, and where the ``craftsroom'' is a punishment cell in disguise. From this Dickensian milieu he elopes with a beautiful girl to honeymoon on an island where the two hope to start their own country. The one person who advocates placing the retarded in homes because her own childhood was ruined by her parents' undivided devotion to her retarded brother is made completely unsympathetic. O'Conner's third may have its heart in the right place, but readers will grow out of patience with its mushiness.