Baron Osvaldo Lambertenghi is forced to sell his ancestral castle to pay his debts.

The manor is ingloriously transformed into a frivolous hotel, and Osvaldo is allowed to continue to live there working as a bellhop.

One day Osvaldo receives a visit from his uncle, Baron Roderico da Frankurten, who turns out to be a real vampire.

Bitten by his uncle, Osvaldo will also turn into a vampire, but his beloved, Lellina, will also be able to free him from the curse.

Uncle Was a Vampire was Christopher Lee's first appearance in an Italian film production.