There is a quadruple murder in San Francisco that baffles the cops on the scene -- it happened in broad daylight on a crowded street with no sign of a struggle. Inspector Dirty Harry Callahan suspects something unusual. He goes to have burgers at the airport with his new partner, Inspector Early Smith. Dirty Harry shoots a couple of incompetent hijackers, and shortly thereafter, he stops a drugstore hold-up. After more killings follow the quadruple murder, City Hall is putting the pressure on the Police Department to put a stop to the killings. At first, Lieutenant Briggs is reluctant to assign Dirty Harry to the case because of Dirty Harry's attitude problem and penchant for pulling his gun, but when the bodies really start to pile up, Dirty Harry is assigned to the case. Whoever is doing the killing seems only to be selecting criminals, like mobsters, murderous pimps, and other felons. Dirty Harry suspects that they have a vigilante on their hands, quite possibly a cop. Discovering that all the killings have been committed by a .357 Magnum, Dirty Harry suspects that Officer Charlie McCoy is responsible. Many cops and the public, people who are fed up with the system, see the killer as a kind of hero. All is not what it seems after Charlie ends up murdered, and Dirty Harry becomes convinced that it's an inside job. As it turns out, a group of frustrated cops led by Officer John Davis have been killing mobsters, murderous pimps, and other people of that kind who are set free. Davis and his three partners Officer Phil Sweet, Officer Red Astrachan, and Officer Mike Grimes killed Charlie to throw off the police from suspecting a conspiracy. Now it's up to Dirty Harry to find Davis and his crew.