The true story of the investigation of the "Zodiac Killer", a serial killer who terrified the San Francisco Bay Area, taunting police with his ciphers and letters. The case becomes an obsession for three men as their lives and careers are built and destroyed by the endless trail of clues.

Deputy Sheriff Lou Ford is a pillar of the community in his small west Texas town, patient and apparently thoughtful. Some people think he is a little slow and maybe boring, but that is the worst they say about him. But then nobody knows about what Lou calls his "sickness": He is a brilliant, but disturbed sociopathic sadist.