The film opens on divorce proceedings involving Ray Reardon, a successful architect, and his first wife. Shortly after their divorce, he agrees to go to a gallery opening to meeta woman with whom his obnoxious friend, Norman, sets him up. While there, he embarrasses himself by bumping into a woman, making her spill wine on herself. She wastes no time verbally abusing him. A week later, he runs into the woman, named Lena Mathers, at the supermarket. She apologizes for her behavior and the two go to dinner. They have sex the next day, marry shortly thereafter, and become parents. Despite his happiness in the marriage, Ray becomes suspicious after catching Lena in several lies about her past. Over time, Ray becomes increasingly paranoid when his wife begins sporting bruises that she will not explain and begins doing things that indicate she is having an affair. During a tense confrontation, Lena taunts Ray by claiming to have had an affair with an unnamed friend of his and refusing to tell Ray if their children are biologically his. Ray hits Lena, who then has him arrested and committed to a mental hospital for observation. Despite an attempt to prove that Lena has been lying, the judge finds Ray to be mentally incompetent and orders him held for six months. Shortly after Ray has been committed, Lena privately admits to him that his suspicions about her were correct all along and that she had planned for years to do what she did to get his money. After Ray convinces one of his friends to tell Lena that she has made a mistake in her "master plan", Lena shows up at his birthday party to talk to him. Ray lures her away from the attendants who are supposed to be supervising him and tells her that having him declared insane was the "mistake" because he could not be held legally accountable for killing her; Ray is now aware that he is genuinely mentally ill and anticipates that after a year of good behavior he would eventually be declared sane and released from the mental hospital. He would then also have sole custody of their children from Lena in her absence. He then strangles her to death on the lawn.
