John Forbes is a family man who's tired of the 9 to 5 humdrum of his job an insurance company executive. Life gets a little more exciting for him when he calls upon femme fatale Mona Stevens. Her boyfriend has robbed a store insured by Forbes' company and has showered her with gifts using the loot. Forbes comes to collect the ill-gotten gifts, but the boyfriend is in jail, and Forbes falls hard for Mona and begins an affair. The only problem is that MacDonald, a private dick who freelances for the insurance company, has had his eyes on Mona first. The obsessed MacDonald turns the soon-to-be-released boyfriend against Forbes.

Insurance agent John Forbes enjoys a comfortable, suburban home life in post World War II, Los Angeles with his wife Sue and son Tommy. He feels, however, that they should have accomplished more and expresses dissatisfaction with his work and social routine. Former policeman turned private investigator J. B. MacDonald has been investigating an embezzler, Bill Smiley, whom Forbes' company, Olympic Mutual Insurance Co., had bonded. MacDonald reports that although the embezzler is in jail, he has traced presents bought with stolen funds to Smiley's girl friend, May Co. model Mona Stevens. MacDonald indicates that he is attracted to Mona and intends to see her again socially. John visits Mona at her apartment and requests a list of presents she has received from Smiley. Mona challenges John's conformity and he responds by inviting her out for a drink, during which they become attracted to each other. Later that evening as he leaves her apartment, he is observed by MacDonald, who has been tailing them. The next day, John finds MacDonald waiting in his office. MacDonald has seen the list of items recovered and asks John about a speed boat that, as a favor to Mona, he has not listed. John then tells Mona he has to take possession of the boat as MacDonald might cause trouble. She thanks him for his help and they begin an affair. When John returns home, he finds MacDonald waiting for him at his garage. MacDonald tells John that he has been following them and emphasizes his continued interest in Mona by beating John up. Meanwhile, Mona discovers that John has left his attache case in her apartment and, in attempting to return it, drives to his house where she discovers he is married. Mona tells John that she wants out, and that he should return to his wife. John does and, for a while, appears more contented. MacDonald continues to bother Mona, even though she tells him that she does not like him and threatens to call the police about him. When he says he will tell John's wife about the affair if she is not "cooperative," Mona seeks help from John, whose response is to beat up MacDonald. In retaliation, MacDonald goes to visit Smiley in prison and tells him about John and Mona. As a result of Mona having returned the misbegotten goods, Smiley is released early from captivity and goes to Mona's apartment. MacDonald has given him a gun and wants him to kill John. Mona then threatens to kill MacDonald should anything happen to either John or Smiley, of whom she is still fond. When Smiley goes to John's house, John shoots him and later claims that it was self-defense against a prowler. When Mona learns of Smiley's death, she shoots MacDonald. John confesses all to Sue and, later, to the district attorney, who tells him that Mona's fate will be determined by whether or not MacDonald survives the shooting. The district attorney lectures John that Smiley's killing, though justified, should have been avoided. After considering divorce, Sue suggests to John that they move to another town and try to rebuild their life together.