OTTO'S BOY by Walter Wager (Macmillan: $16.95). There's a new kind of maniac stalking New York streets, and he's got enough nerve gas to make the Big Apple into a ghost town. To show he's sincere, he begins by murdering 117 people in a crowded subway car. Hunting the killer--when not skirmishing with headline-hungry bosses or recalcitrant federal bureaucrats--is a bright and brave maverick cop. The maverick cop has two faithful sidekicks. And he develops a relationship with a beautiful female psychiatrist he consults regarding the killer. The characters, as you might guess, are somewhat predictable. The villain, for example, is not just a psycho demanding money. He's also a racist son of a Nazi, with sexual hangups. Still, the book moves along as briskly as a subway car without brakes. Tension is built effectively as the nerve-gas-toting maniac prepares a toxic goodby for New York. This is the kind of thriller you can pick up at an airport bookstall and it will keep you occupied better than most in-flight movies.