Family Plot is the tale of Madam Blanche (Barbara Harris) who works deceptively as a psychic even though she has no abilities as a medium. She is in a relationship with George (Bruce Dern), who works as a taxi driver and helps out Blanche in her schemes to scam the grieving. One day a widow named Julia Rainbird (Cathleen Nesbitt) tasks the two with finding her long lost nephew who was abandoned after a great public scandal involving her family. All goes according to plan until Blanche and George come in contact with Arthur Adamson (William Devane) and his girlfriend Fran (Karen Black), and the two couples realize that they are involved together in the same mystery.