The movie opens on divorce proceedings involving Ray Reardon (Spader), a successful architect. Shortly afterwards, he agrees to go to a gallery opening to meet a woman that his obnoxious friend, Norman (Larry Miller), sets him up with. While he is there, he embarrasses himself by spilling wine on a woman (Amick) who wastes no time verbally abusing him. A week later, he runs into the woman, named Lena, 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 that she is having an affair. During a tense confrontation, Lena taunts Ray by claiming to have had an affair with his friend 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 admits that his suspicions about her were correct all along and that she did 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 a mistake because he could not be held legally accountable for killing her. He then strangles her to death on the lawn.