In 1971, San Francisco faces the terror of a killer maniac known as the "Scorpio" (Andrew Robinson), who snipes at innocent victims and demands ransom through notes left at the scene of the crime. Inspector "Dirty" Harry Callahan (Clint Eastwood) is assigned to the case along with his newest partner Inspector Chico Gonzalez (Reni Santoni) to track down Scorpio and stop him. Using humiliation and cat-and-mouse type of games against Callahan, Scorpio is put to the test with the cop with a dirty attitude.