The film opens with a striking visual of a Smith & Wesson Model 29 revolver against a red backdrop, accompanied by the ominous voice of Inspector 'Dirty' Harry Callahan (Clint Eastwood). He declares, "This is the .44 Magnum, the most powerful handgun in the world. And it could blow your head clean off. Do you feel lucky?" As the credits roll, the story sets a dark tone, revealing the aftermath of a heinous crime involving Carmine Ricca (Hal Holbrook), a labor racketeer who escapes justice. Following his acquittal for the murder of a union leader and his family, Ricca's freedom ignites fury among protesters outside the courthouse.
Meanwhile, a San Francisco Police Department motorcycle cop, who is later revealed to harbor a vengeful persona, witnesses the chaos and takes matters into his own hands. He pulls over Ricca's limousine under the guise of issuing a ticket but swiftly turns the encounter deadly, executing all occupants: Ricca, his attorney, and their driver in cold blood.
As the narrative unfolds, Harry and his partner, Early Smith (Felton Perry), are drawn into the investigation amid tensions with Lt. Neil Briggs (Mitch Ryan), who loathes Harry's maverick style. Harry, unimpressed by the bureaucratic constraints, exclaims, "A man's got to know his limitations." This friction hints at the philosophical clash between traditional law enforcement and a more brutal approach to justice.
Amidst escalating violence, a chilling scene unfolds at San Francisco International Airport, where Harry dons a pilot's uniform to thwart a hijacking. This not only showcases his resolve but also deepens his rivalry with Lt. Briggs, who is forced to acknowledge Harry's effectiveness despite his disdain for Harry's methods.
The plot thickens as Harry encounters rookie cops, notably Philip Sweet (Tim Matheson), John Davis (David Soul), Donald "Red" Astrachan (Kip Niven), and Michael Grimes (Robert Urich),who share a camaraderie that history suggests may be tested by the rising tide of violence. Their camaraderie is juxtaposed against the backdrop of an emerging vigilante, the motorcycle cop, whose ruthlessness escalates following a slaughter at a gangster's swimming party.
As the vigilante's audacious killings prompt Harry to confront corruption within the force, he grapples with a profound moral quandary. The unidentified cop who carries out the executions soon reveals himself as John Davis, thrusting Harry into a web of deception and betrayal.
Climbing the tension to a climactic confrontation, Harry's investigations lead him to the realization that the law he cherishes may be intertwined with moral ambiguity. Tragedy strikes when Harry's ally, Charlie McCoy (Mitch Ryan), is killed, propelling Harry into a determined pursuit of justice.
The final confrontation showcases the deadly stakes of Harry’s commitment to his principles as he faces off against both the corrupt police force and the killers. In an explosive climax, following several harrowing encounters, Harry confronts Lt. Briggs, revealing the complexity of loyalty and the price of justice in a world marred by corruption.
As the narrative winds down, Harry’s chilling acknowledgment of the consequences of his choices echoes the film's darker themes. He resolutely states, "I'm afraid you've misjudged me," ultimately cementing his struggle against a system he both serves and despises. The film ends with him walking away, a true embodiment of the saying, "A man's got to know his limitations," leaving audiences pondering the costs of moral integrity in a corrupt world.
