An eccentric and macabre aristocratic family, known for their unique and morbid flair, leads a reclusive life in a vast, dilapidated mansion. Amidst their graveyard picnics and other unconventional antics, the family is unaware that their lawyer is scheming to defraud them. Capitalizing on their naive but benevolent nature, the lawyer devises a plan to introduce someone who can impersonate a long-lost relative. The intention is to gain access to the family's vast fortune by inserting this faux relative into the household.

The scheme unfolds when the lawyer introduces a man claiming to be the family's missing uncle Fester, who had disappeared 25 years earlier under mysterious circumstances. Initially met with skepticism, the faux Fester manages to convince the family of his identity, particularly winning over the children with his peculiar but seemingly familial ways. The mother, with an intuitive sense that something is amiss, harbors doubts about this supposed brother-in-law's authenticity. Meanwhile, the rest of the family, including the passionate father and their morose daughter, gradually accept him, drawn to the qualities that echo their dark and endearing personalities. As the plot progresses, the strain between trusting kinship and rising suspicion stirs a dynamic tension within the family's ranks.