A group of the town's leading citizens is acting as a vigilante committee, kidnapping, trying, and executing suspects who have been acquitted of crimes. Shaft becomes involved after the group goes even further, killing an attorney who helped get him started in his business.
Shaft gets into an altercation with a procurer while trying to protect an old girlfriend who has fallen on hard times and turned to prostitution. When the procurer is found murdered, Shaft is accused of the crime, and the girl is his only alibi, but she has disappeared.
Shaft is hired to prove the innocence of a young man accused of an accidental hit-and-run killing with a stolen car. He finds that the victim was a casino enforcer who was trying to skim off his employer, and that his killing was probably not an accident at all.
A banker's wife is kidnapped, and the kidnappers insist that Shaft deliver the ransom. But complications arise when, on the way to the drop point, Shaft is stopped by an overzealous deputy who won't listen to a word he says.
A police officer is framed for extortion and assault on a singer. He tells Shaft he believes this was done to prevent him from uncovering crooked officers involved in an auto theft ring. Shaft persuades Rossi to go undercover to investigate, but when Rossi is shot down and lies near death, Shaft feels responsible and tries to break the ring himself.
A business executive under suspicion for embezzlement is killed, and his wife injured, after a fire engulfs his office. The wife hires Shaft to investigate, as the fire is determined to be arson. But all is not as it seems, and more murders occur as an associate of the executive tries to get control of the company and retrieve a diamond necklace that was put in a safe deposit box.
A grand jury witness, who was to testify against a mobster, is killed by a grenade at the courtroom. Also killed is a friend of Shaft who was at the courtroom to get married. Shaft is determined to catch the hit man, who he briefly saw, and decides to set himself up as a decoy to do so. The killer is also a devoted family man whose wife is catching on to what he really does for a living.