In Los Angeles, California, architect Paul Kersey has been dating newspaper reporter Karen Sheldon for two years. Paul also employees Karen’s seventeen-year-old daughter, Erica, as an intern in his firm, Paul Kersey & Associates. One night while Paul and Karen have dinner, Erica goes with her boyfriend to an amusement arcade where they both buy small bags of cocaine. A few hours later, Erica dies from a drug overdose. The next night, Paul follows Erica’s boyfriend to the arcade. The boyfriend confronts his drug dealer, JoJo, who stabs him in the stomach, killing him. When Paul arrives, JoJo runs away, but Paul shoots and kills him. Paul is summoned to the home of millionaire Nathan White, who wants to hire him because of his history of vigilante justice. White reports his beloved daughter, Lisa, died of a drug overdose last year, shortly after starting college. White has collected information about the major illegal drug organizations in Southern California and now wants Paul’s help to stop them. Paul says he needs a few days to think it over. After Erica’s funeral, Karen blames herself for not knowing her daughter was using drugs. Paul suggests she channel her grief by doing an investigative piece for her newspaper. Karen pitches the story to her editor, who reluctantly agrees. Karen goes to the coroner’s office to look at the bodies of teenagers who died from drug overdoses, then goes to the arcade trying to buy information. One of the dealers says the kind of information she wants will cost her a lot of money. Paul agrees to work for Nathan White, who tells him that two gangs control ninety percent of the illegal drugs in Southern California, the Zacharias gang, led by Ed Zacharias, and the Romero gang, led by brothers Jack and Tony Romero. A year before, the Romeros tried to invade the Zacharias territory and a gang war erupted. Ed Zacharias negotiated a truce, but tensions could explode at any time. Meanwhile, police detectives Reiner and Nozaki receive a ballistics report noting the bullet that killed JoJo matches the gun used in a vigilante shooting two years earlier. Witnesses at the arcade gave a description of Paul’s car and a partial license plate number, so police go to question him. Paul lies, saying he was at home on the night of the shooting and does not own a gun. Paul poses as a bartender working a party at Ed Zacharias’s Hollywood Hills home. When Paul slips away to plant bugs in the telephone, he overhears Zacharias and the Romeros talking, each side saying they want to maintain the peace. He also sees Zacharias murder a man who was skimming drugs from the shipments. When Paul accidently makes a noise, Zacharias’s men try to kill him, but he escapes. Paul plants an explosive in a bottle of wine, then gives the bottle to some Romero gang members, who are killed when it explodes. Later, Paul kills another of the Romero men who operates out of a video store and sends another Romero man flying off a high-rise balcony to his death. At a fish cannery in San Pedro, California, Paul also shoots up Zacharias’s backroom drug operation. Police believe these deaths mean the gang war is starting up again and tell detectives Reiner and Nozaki to forget about the vigilante case for now. However, Nozaki recognizes Paul’s car at one of the crime scenes and realizes he is the vigilante. Nozaki goes to Paul’s office, announcing he is working for Zacharias and wants to know who hired him. When Paul refuses to answer, Nozaki tries to shoot him, but Paul fires first, killing him. After police find Nozaki’s body dumped on a hiking trail, Detective Reiner discovers the Department of Motor Vehicles records linking Paul to the vigilante murders. Ed Zacharias arranges a meeting with the Romero brothers at an oil field where he tries to explain that someone is setting them up. From a nearby hill, Paul opens fire on them. The two gangs start firing at each other and soon both sides are dead. When Paul arrives at a deserted field for an appointment with Nathan White, the chauffer says he is supposed to drive Paul to the meeting. But after Paul gets in the limousine, the chauffer walks away and Paul realizes he is locked inside the car. He shoots out the back window and crawls out just before the car explodes. Paul goes to Nathan White’s mansion to confront him, but the man there is not who Paul has been dealing with. This man, the real Nathan White, says he has been in Europe for the past three months and Paul realizes he has been set up. Police pull over Paul’s car and arrest him for murder. However, when they start driving in the opposite direction from the police station, Paul realizes they are not real policemen. He distracts the fake cops and they wreck the car, as Paul escapes. The fake Nathan White makes plans to take over the region’s drug operations now that the Zacharias and Romero gangs are dead. When he learns that Paul is still alive, he has Karen Sheldon kidnapped. Detective Reiner waits at Paul’s house to arrest him, but before he can take Paul in, the fake Nathan White telephones, saying he has Karen. Paul knocks Reiner unconscious, grabs some high-powered weapons and goes to a designated parking garage. White’s men shoot Paul’s car, only to discover he is not inside. Paul starts shooting at them, killing several of White’s men. White escapes to a roller skating rink and Paul follows. A shoot out ensues, but White escapes with Karen as his hostage. When Karen breaks free, White shoots her in the back, killing her. Paul fires a bazooka at White, killing him. Reiner comes upon the scene and tries to arrest Paul, but the vigilante just walks away and Reiner does nothing to stop him.