Undoubtedly authentic in word, deed and attitudes, but not really reaching where it's preaching -- this case of three young policemen of the Los Angeles force confronting the coming debacle, or what is called here, the "dying" of the "don'ts." The job of enforcing the don'ts gives the men direction and purpose, although Serge, Gus and Roy begin their careers with constricting hang-ups: Serge is reluctant to admit his Mexican background; Gus, a small man, fights a fear of cowardice; and Roy, a "liberal," lawdhelphim, is blinded by arrogance. But all three work their ways through to stability, including Roy before he is killed. The route passes from cruising apprenticeships, to nights on the vice squad, routine pinches and calls, and finally violent race riots. The author surely must have put in considerable mileage in the squad car, but because of the rush to proselytize, it's a little skimpy on fictional substance.