Kate Miller (Angie Dickinson) is feeling unsatisfied with her marriage, so she begins to see psychologist Dr. Robert Elliot (Michael Caine), who instructs her to be upfront about her feelings to her husband. Conflicted, Kate visits a museum where she meets a man and sleeps with him. Riding the elevator down from his apartment, she is brutally murdered by a mysterious blonde woman. Liz Blake (Nancy Allen), a Manhattan hooker, witnesses the murder and soon finds her own life to be in danger from the killer. Liz and Kate's son, Peter (Keith Gordon), team up to see if they can figure out the identity of the mysterious woman.