The City by the Bay faces the terror of a serial killer known as Scorpio (Andrew Robinson), who viciously snipes at innocent victims and demands ransom through notes left at the scene of the crime. Inspector Dirty Harry Callahan is assigned to the case along with his newest partner, Inspector Chico Gonzalez (Reni Santoni) to track down Scorpio and stop him. Using humiliation along with cat and mouse games against Callahan, Scorpio is put to the test by the cop with the very dirty attitude.