After two relentlessly mediocre comic novels (The Greening of Thurmond Leaner, and this year's dismal ""M.H."" Meets President Harding), Zagst surprises with the rather affecting tale of a Houston executive driven to a nervous breakdown. It's 1975, and Al Sprayberry, still on the lighter side of 30, is a gung-ho executive for Parkland Life and Casualty, selling advertising time to TV stations. Slowly, however, his life takes a turn for the worse: he develops a horrible case of tapeworm, becomes certain his cute, ex-cheerleader wife, Terri, is having an affair with her running instructor, and decides that he can't stand the garish preparations for the forthcoming Bicentennial. He becomes obsessed with reruns of old shows like ""The Rifleman,"" seeing Lucas McCain's confrontations with bad guys in classical terms of good and evil. Then, after finally going completely nuts at a board meeting attended by powerful New York executives, Sprayberry is committed to a mental asylum that in the Texas hill country consists of an entire town in the middle of a lake. There he finally regains his sanity, and becomes such a model prisoner that he can make a stirring plea for better mental-health care when Rosalynn Carter comes for a visit. Sprayberry finally escapes--by this time, no one cares--and makes his way to an idyllic island off the coast of Mexico, where he is able to come to grips with the world. Divorced from Terri, he returns to Parkland Life and goes back to his old job, believing in ""the fragility of the human mind, and. . .and attitude of patience, forgiveness, compassion, and hope."" Overlong at times, and cutely simplistic in the Vonnegut mode--but in Sprayberry, Zagst has created a character whose plight succeeds in moving the reader.