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