Spenser is a Private Detective who is hired by a woman to watch her sister and protect her from an old boyfriend. Susan Silverman is Spenser's girlfriend, a research assistant in a psychologist's office. Susan is elated to have been chosen by handsome Dr. Ed Howard from all the other research assistants to accompany him to San Francisco for a psychology conference. Spenser is less elated. Ed Howard enters the picture when Spenser realizes that his client has multiple personalities, she is herself and her sister. Or is she her sister and . . .she's both Diane and Donna, ok? Susan points out that this is Howard's speciality and should be the one to counsel the woman. Spenser is less than elated to bring in the doctor.