San Francisco Police Inspector Harry Callahan returns in the third of the Dirty Harry movies. Teamed with his new partner, Policewoman Inspector Kate Moore, they hunt for a group of terrorists that are blackmailing the City of San Francisco for two million dollars.
Robbers at a liquor store are holding a shopkeeper and three of his patrons hostage. Asked by the robbers for a car with a police radio, Inspector Dirty Harry Callahan volunteers his own car. Dirty Harry drives the car right through the store's plate glass window. Before the robbers know what hit them, Dirty Harry has shot them. $14,379 is how much the San Francisco police department will have to pay to repair the damages caused by Dirty Harry's encounter with the robbers. Rather than getting a medal, which he doesn't want, Harry is relegated to Personnel to help interview patrol officers on the list to make inspector. Dirty Harry is told that of the eight openings, three will be filled by women. A group that calls themselves the People's Revolutionary Strike Force (PRSF), led by Bobby Maxwell, are making plans to go on a rampage throughout San Francisco as some kind of extremist political statement. When Dirty Harry's longtime partner is killed by the PRSF during a major weapons theft, Dirty Harry vows revenge and, surprisingly, is given some support by his superiors. Dirty Harry has bad luck when it comes to partners. Being Dirty Harry's partner is like having your doctor say you only have a few days left to live. Harry gets a new partner named Kate Moore, a woman whose decade long entire police career has been spent in the Human Resources department. With her suit and high heels, Kate has trouble chasing suspects. But she proves to be resilient and resourceful and becomes Harry's friend. The PRSF continues stealing explosive devices and rocket launchers. After they're armed to the teeth, they kidnap the mayor and demand a ransom of two million dollars. The PRSF is prepared to blow up the toilets in the police station itself. Dirty Harry goes undercover, attempting to root out Maxwell and his crew. Kate and Dirty Harry discover that the mayor is being held at Alcatraz Island. This leads Kate and Dirty Harry to a showdown against Maxwell.
Following a reprimand from his superiors for his somewhat destructive approach to his work, Harry Callahan finds his new partner to be female. Though none too pleased with this, the job has to come first - in this case the City being held to ransom following an arms robbery, by a gang prepared to blow up the toilets in the police station itself.
When SFPD Insp. Harry Callahan ends a liquor store holdup by doing things in his usual hard-boiled manner, his bleeding-heart boss, Capt. Briggs (Bradford Dillman) demotes Harry to the personnel division. But Harry doesn't remain there for long, as a group of terrorists rob an arms warehouse and begin a bloody extortion spree demanding $2 million from the City. Harry is paired with Insp. Kate Moore (Tyne Daly) to shut the terrorists down. Callahan is none too thrilled to be paired with Moore, but she more than proves herself when she and Harry pursue the terrorists to their hideout in the old prison of Alcatraz.