Neighbors can be a hazard in Manhattan, particularly if you have to sit and watch a husband almost murder his wife on the next terrace, during the cocktail hour yet. Mac is just an ordinary old Assistant D.A. when this happens to him in a case which soon has one presumably dead spouse and a substantial inheritance passed on to wife and lover. But oddly after the fact arrive two thugs and two gorillas (one real. . . one monkey suit) in a discotheque aptly named The Big Banana. The plot is slick and slippery all right and it's the fancy footwork that keeps you guessing.