After an idyllic Hawaiian vacation, design consultant Paul Kersey and his wife Joanna return to their apartment in New York City. A few days later, as Paul settles back into work at Blueridge Corporation, Joanna, joined by their married daughter Carol, goes grocery shopping at the local market, unaware that they have come to the attention of three restless young thugs. When Joanna requests the groceries be delivered, the young men secretly get the Kersey address from the boxed items, then follow the women there. Sneaking into the secure building through a delivery entrance open for some movers, the thugs go to the Kersey’s and, pretending to be delivering the groceries, gain access to the apartment. There, they beat Joanna senseless and rape and batter Carol. That afternoon, Paul is stunned to receive sketchy news of the assault from Carol’s husband, Jack Toby, and meets his son-in-law at the emergency room where the men learn that Joanna has died from the beating and Carol remains in profound shock. After Joanna’s burial in Connecticut, Paul returns to the apartment and upon returning to work his boss, Ives, offers him a project in Tucson. Uncertain, Paul asks to think it over and meanwhile visits the police station to inquire about progress on the assault investigation. Disturbed when the investigating detective admits that Carol’s continued uncommunicative state has hindered any chance of identifying the attackers, Paul returns home. On visiting the bedridden, unresponsive Carol a little later, Paul learns from Jack that doctors have advised that Carol be kept away from anyone reminding her of the assault. Frustrated that he reminds his daughter of Joanna, Paul nevertheless agrees to stay away temporarily and accepts the job in Tucson. Walking home from the bus stop that evening, Paul is nervous about strangers around him, and when a man comes up behind him and demands money, Paul swats him with a sock filled with a roll of quarters. Surprised when the would-be mugger runs away, Paul returns home, oddly elated. Arriving in Tucson a few days later, Paul is met by client and realtor developer Aimes Jainchill. On their way to Jainchill’s office, the men stop at a “Wild West” movie location tour where a confrontation between bandits and a sheriff is reenacted by stunt men. Paul finds himself quietly pleased when the sheriff overpowers each bandit with a large shotgun. Over the next few weeks, Paul buries his grief by working long hours on Jainchill’s housing development project, taking into consideration his client’s strict admonition that the project be in synch with the natural physical surroundings. One night, Jainchill finds Paul working late and, sensing his tension, invites him to a gun club that he frequents. At the shooting range, Paul amazes Jainchill by admitting that he was a medic and conscientious objector during the Korean War. However when Paul scores a bullseye on the target, he admits that he grew up with guns until his father was killed in a hunting accident. Impressed by Paul’s proficiency, Jainchill offers him the chance to shoot an 1890 “hog leg” Colt .32. After Jainchill approves Paul’s completed design for the property, he gives Paul a going away present before Paul returns to New York. Met by Jack, who has been in constant contact reporting Carol’s condition, Paul is distressed to discover that Carol has fallen into a catatonic state and been hospitalized. Reluctantly, Paul agrees with Jack and Carol’s physicians that she should be institutionalized. At his apartment, Paul opens Jainchill’s gift and discovers that it is the Colt pistol. A few nights later, Paul walks home through an empty stretch of the park where he becomes aware of a man trailing him. When the man rushes Paul and demands money, then pulls a gun, Paul pulls out the Colt and shoots him. Returning home afterward, Paul collapses in anxiety and is sick over the attack. When the mugger dies of his wound, detective Frank Ochoa is assigned to investigate. The next day, Paul takes the pistol in its leather case to his office where he reads the newspaper account of the attack and learns that the mugger had a long criminal record. Walking home some evenings later, Paul passes an alley just as three men finish beating and robbing a man. Although the men threaten Paul with a gun, knife and crowbar, he unflinchingly shoots all three. A few days afterward, Paul accompanies Jack to a mental rehabilitation center in the country where they place Carol. Reflecting that if they lived there and not the city, there would never have been an attack, Jack is puzzled when Paul wonders about what has happened to the country’s pioneering quality of self-reliance and reminds him that those days are long passed. Meanwhile, on a hunch, Ochoa orders his staff to investigate all war veterans whose families have endured a recent criminal attack. Over the next few nights, Paul purposely wanders the subways and parks in search of criminals and when two men attempt to mug him in an empty subway car, he shoots them and, leaving behind his bag of groceries, gets away without notice. Soon after, the police commissioner gives a news conference asking the killer, dubbed “the Vigilante” by the press, to give himself up. When questioned whether the recent abrupt drop in crime is connected to the vigilante’s activities, the commissioner refuses to comment. While Ochoa’s team examine the bag of groceries left behind by Paul on the subway, Jack visits Paul and is disconcerted by his father-in-law’s cheerfulness and refusal to pine over Carol. Later, Paul again goes in search of criminals and is cornered on an empty subway platform by two men wielding knives. After Paul shoots one of the men, the other manages to slash Paul in the back of the shoulder before Paul shoots him. The injured man flees up to the street where he quickly is discovered and taken to the hospital by police while Paul returns home to tend to his own wound. Learning that the groceries from the subway attack were purchased some miles from the subway shooting, Ochoa concludes that the vigilante is purposely going in search of criminals. When Paul’s name comes up in the investigation of veterans whose families have endured a recent criminal assault, and the groceries are traced back to the store frequented by the Kersey’s, Ochoa orders him followed. Exploring Paul’s apartment while he is at a party the next night, Ochoa finds blood stained cotton swabbing and several newspapers and magazines devoted to the vigilante murders. Responding to a summons from the district attorney, Ochoa meets the commissioner there and reports that Paul’s blood sample matches that taken from the attacker’s knife blade, thus confirming Paul as the vigilante. To Ochoa’s surprise, the district attorney orders him not to arrest Paul as the crime rate has continued to drop, but instead warn him off. Although Ochoa telephones Paul to tell him that he his being followed, Paul nevertheless sneaks out the back of his building to return to his office to retrieve the Colt. Upon realizing that Paul had sneaked out of his apartment, Ochoa follows him, but does not reach him before Paul has confronted three muggers in the park. Shooting two, Paul then chases the third into a warehouse, where, exhausted from blood loss from his reopened wound, Paul demands the confused mugger “draw” before collapsing. Later at the hospital, Ochoa tells the recovering Paul that if he will request a transfer to Chicago, the detective will destroy the Colt and he will not be prosecuted. Some time later, Paul arrives at the Chicago train station where he assists a young woman and her daughter who have been harassed by some punks. As the young men taunt him from a distance, Paul cocks his hand in the shape of a gun and pointing it at them, smiles.