Three seemingly unrelated murders happen in Sacramento a month apart. After he and his partner are unable to solve the third, Police Homicide Detective Sergeant Harold ‘Harker’ Smith meets with his supervisor, his former partner, Captain Dennis Steele, and reports his belief the murders are related by motive.
One murder victim that put his wife in the hospital with his fists was beaten to death. Another man that killed a child while drunk driving was run over repeatedly with his own vehicle. A third man that had made a video of himself abusing and killing his puppy was hanged by a leash in a dog park.
Smith tells Steele he believes there is a serial killer loose in Sacramento, a vigilante that retaliates for people unable to do so themselves.
The murders continue and continue to baffle Smith and his partner, Detective Roberto Alcarez.
A gangbanger accused of a drive-by killing of a little girl is used for target practice.
A man that drowned his wife is found drowned.
A man that broke his son’s arm is found dead with forty-two broken bones.
Smith and Alcarez eventually conclude the vigilante might be a police officer, but their chief won’t let them pursue the morale busting lead.
The FBI declares there are thirty-five to fifty serial killers loose in the country at any one time. Smith caught the Steamroller Killer, and he and Alcarez caught the Rude Men Killer, but the Vigilante leaves no clues.