A synopsis stopping just short of full plot spoilers:
In director Gene Fowler, Jr.'s "Gang War," tough guy Charles Bronson plays Los Angeles high school math teacher Alan Avery who finds himself in the wrong place at the wrong time. Big-time mobster Maxie Mathews (John Doucette of "The Big Heat") has dispatched his second-in-command, Joe Reno (Jack Reynolds of "The Basketball Fix"), and his henchman, Bernard "Axe" Duncan (Ralph Manza of "Get Shorty"), to take care permanently of Slick Connors (Leonard P. Geer) who has since become an informant for the authorities against Maxie. Reno and Bernard trap Slick atop a car and stab him to death.
Alan Avery witnesses this brutal mob killing on his way home from picking up a prescription for his wife. Later, the police show up at Avery's residence where he lives with his pregnant wife, Edie Avery (Gloria Henry), and they hand him his wife's prescription.
Avery has no problem with testifying against the mobsters who killed the man. A corrupt cop makes certain that the media knows everything there is to know about Avery, and the newspaper the following day features a banner headline about Avery's involvement. Naturally, mob kingpin Maxie Meadows wants to throw a scare into the public-spirited school teacher so he sends his manservant, Chester (Larry Gelbman of "She Demons") a former pugilist over to Avery's house to soften up the wife and throw a scare into Avery. The former prizefighter lays into Edie, and Alan comes home to find the tea kettle whistling stridently and his wife dead on the floor.
Immediately, Avery arms himself with an automatic pistol and takes a taxi out to Mathews' residence where he lines up the racketeer in his sights to shoot him.