When a madman calling himself "the Scorpio Killer" menaces the city, tough as nails San Francisco Police Inspector "Dirty" Harry Callahan is assigned to track down and ferret out the crazed psychopath.
Mobster Carmine Ricca (Richard Devon) drives away from court in his limo after being Acquittal of a mass murder on a legal technicality. However, while his limo is on an isolated road, Ricca and his three associates are murdered by an San Francisco Police Department Police officer. Inspector Harry Callahan (Clint Eastwood) visits the crime scene alongside his partner Earlington "Early" Smith (Felton Perry), despite the fact that the two of them are supposed to be on stakeout duty. Callahan trades barbs with their superior, Lieutenant Neil Briggs (Hal Holbrook). After he and Early stumble upon and foil an attempt to hijack an airliner, Callahan meets rookie cops Phil Sweet (Tim Matheson), John Davis (David Soul), Alan "Red" Astrachan (Kip Niven), and Mike Grimes (Robert Urich) while practicing at an indoor firing range. Callahan deduces that Sweet is an ex-United States Army Rangers and Special forces veteran after loaning his gun to the rookie, being very impressed by the rookies. Sometime after, a motorcycle cop slaughters a mobster's pool party using a satchel charge and a submachine gun.
In Marin County, two gas company men are lured by a scantily-clad woman to a remote spot in Mill Valley and killed by Bobby Maxwe. Maxwell's gang, the People's Revolutionary Strike Force, plans to use the gas men's uniforms and van as part of an ambitious series of crimes that will make them rich.
A rape victim is exacting revenge on her aggressors in a small town outside San Francisco. "Dirty" Harry Callahan, on suspension for angering his superiors (again), is assigned to the case.
San Francisco Police Department Inspector Harry Callahan's testimony against crime kingpin Lou Janero puts the mobster in prison. Callahan becomes famous and the target of Janero's men, both of which he dislikes. After Callahan kills four attackers during an ambush, the department assigns Al Quan as his partner; Callahan advises him to get a bulletproof vest, as his partners often get killed. They investigate the heroin overdose death of rock singer Johnny Squares, found in his trailer during filming of a slasher film directed by Peter Swan at the Port of San Francisco. We see that his death was not a typical overdose, but is actually murder.