The film opens with a grand view of Los Angeles, with a news broadcast in the background detailing an increase in crime in the city. The overview of the city goes until the end of the opening credits where we zoom in on the new house of Paul Kersey where the maid, Rosario (Silvana Gallardo), is preparing dinner. He seems to have picked up the pieces of his life to move on, as his girlfriend is KABC news/radio reporter Geri Nichols (played by Bronson's real-life wife Jill Ireland) and they both go and pick up Carol from the hospital and spend the day with her. Paul talks to the doctor and while she is still in her catatonic state, she recently spoke five words. Paul, Geri, and Carol spend the rest of the afternoon at a carnival, where Paul offers to buy ice cream while the girls look around. While waiting in line for some ice cream, he gets mugged and his dollar bill is stolen. At first Paul doesnt mind but realizes they also took his wallet. Paul manages to catch up with one of them (Jiver), but Jiver exclaims that he wasnt the one who took the wallet. Geri heads to do an interview with the senator while Carol and Paul go on a boat ride. The same six muggers who stole Kerseys wallet arrive at his house and rape Rosario. Paul arrives home with Carol, only to get beaten unconscious. Rosario tries to call the police, but the thugs hear the sound and quickly kill Rosario. They then take Carol to their hideout, where they rape her. After the attack, she escapes and jumps from a window, only to get impaled on the railings below. Geri arrives to the house as Paul regains consciousness and the police arrive. Lt. Mankewicz (Ben Frank) is one of the first on the scene, asking Paul about the identification of the muggers because the description was a little vague. A short time later, Paul learns about the death of his daughter and is sent to the station to ID her. Later on Mankewicz asks Paul to view some photos at the station to rejog his memory, to which Paul declines by saying it wont do any good.
The next scene is at a funeral where Paul and Geri both attend. That night, Paul pulls out his gun, changes clothing, and rents a low-rent apartment as his base of operations. The next night, he spots Stomper and follows him as a drug deal is about to be made. Kersey tries to be quiet as he can, but the others notice his presence when he knocks over a can. Kersey kills one of them, then orders the other two out of the room where he kills Stomper.
The following evening as he is patrolling the streets, he hears a scream coming from a parking lot where a man and a woman are being assaulted by four muggers: one of the muggers is Jiver, whom Kersey chased down the alley the day of his daughters death. He kills all but Jiver who manages to get away, but is later wounded. Paul follows the trail of blood, and manages to wound the Jiver again before he kills him. The LA police quickly hear about the muggings, as does the NY Police Department. Detective Frank Ochoa is called by LA precinct to help. The Commissioner thinks the vigilante killings may be done by Kersey again. Fearing that Kersey, when caught, will reveal that they let him go instead of prosecuting him, the NYPD sends Inspector Frank Ochoa to make sure that doesn't happen. Ochoa meets with Lt. Mankewicz, who suspects that Frank is hiding something.
That night, he breaks into Geris apartment and notifies her about his recent vigilante spree. Geri later confronts Paul, but quickly denies it. Paul drives Geri to work the next morning, where Ochoa is waiting. In order to keep tabs on Paul, Frank calls Mankiewicz and asks him to park his car near his apartment (but he doesnt tell Mankiewicz about following Kersey himself). Ochoa follows Kersey to an abandoned park, where a major narcotics ring goes down - including four of the surviving six members: Cutter (Laurence Fishburne), Plunkett (E. Lamount Johnson), and Nirvana (Thomas Duffy). Ochoa sees Paul from a distance hiding in a bush, but decides to help Paul after detecting a spotlight heading in his direction. Warning Paul, Ochoa quickly dispatches him with a shot. Paul runs behind a tree as men grab their guns and fire back. Ochoa gets shot by a hail of gunfire, but Paul manages to kill Cutter and Plunkett. Paul also shoots and kills the getaway driver, who plummets off a cliff to a fiery doom below. The final mugger, Nirvana, gets away and later has a confrontation with police. Paul goes over to Ochoa and asks him why he saved his life. Ochoa says it was either them or me, and wants Paul to kill Charles for him. Ochoa dies as police arrive and Paul escapes into the night. The police get the name of Ochoas killer by a badly injured Plunkett, who later succumbs to his injuries and dies.
Charles Wilson is later arrested and tried after a police confrontation, in which Paul narrowly misses his opportunity for a kill, but is sent to McLarren State Hospital. Geri and Paul visit the hospital, in which Paul acquires a doctor uniform. Paul later has lunch with Geri the next day and proposes to her. Geri accepts. That night, along with his fake doctors ID, Kersey visits the hospital and gains access to Wilson. Wilson and Kersey have a violent confrontation, and Kersey is stabbed repeatedly by Wilson. Wilson slams Kersey up against an electric machine, but Kersey ducks the oncoming punch. Wilsons hand smashes through the machine as Kersey wastes no time in turning it on. Donald Kay, the head orderly on duty, witnesses Wilsons death, but sympathizes with Kersey: he gives him three minutes to escape before he pulls the alarm, which he does.
Geri goes to his apartment later that night and finds the scanned copy of the stolen ID. Geri realizes that he is the killer after she hears a report of Wilsons confirmed death on the radio. She puts the paper and the engagement ring on the table and drives off. Paul arrives home to an empty apartment after Geri drives away. The ending of the movie has Paul speaking to the boss about a party in celebration of a new architectural design. His boss Elliott Cass (Michael Prince) invites him to a party and Paul answers when asked if he is free, What else would I be doing?
