After being the repeated victim of harassing phone calls, Helen Clarvoe asks a lawyer Paul Blackshear to investigate a woman named Dorothy Johnson who may be behind the calls. Dorothy blames Helen for the break-up of her wedding engagement. Paul investigates further and begins to believe that Dorothy is a murderer. Paul believes that Dorothy killed a photographer she once posed for. Apparently Dorothy was very upset about a number of pictures he took of her. Later, however, Paul gets a phone call from Helen who tells him that Dorothy broke into her apartment and is holding her hostage at gunpoint. Paul calls the police and heads over to Helen's apartment. Outside the apartment, Paul hears Helen and Dorothy having an argument inside. Paul, however, is stunned when another woman arrives claiming to be Dorothy. Helen is suffering from multiple-personality disorder. She has been pretending to be Dorothy out of guilt over what she once did to her and has been insanely trying to get even with herself.