Baron Osvaldo Lambertenghi (Renato Rascel, who represented Italy in the 1960 Eurovision contest and acted in several films) has sold his ancestral castle and stays on as a porter, which he does without complaint until the day that his uncle Baron Roderico da Frankurte (Christopher Lee) arrives.
Roderico is a vampire, in case you didn’t read the title. Osvaldo tries to tell the guests, but they think he’s crazy, at which point he gets bitten too. This was made nearly instantly after Hammer’s Horror of Dracula and if he wasn’t a big enough box office star to get people to show up, Sylva Koscina from Hercules is here as well. So is Susanne Loret (Atom Age Vampire), Kai Fischer (The Hellfire Club) and Lia Zoppelli (who was in Toto and Cleopatra) are also on board.
Director Steno is mostly known for comedy films, like his films with Toto, Banana Joe with Bud Spencer, Dr. Jekyll Likes Them Hot with Edwige Fenech and Man, Beast and Virtue, which had Toto and Orson Welles in the same movie.
For Hammer fans, you can almost consider this a lost Lee Dracula, except that the humor and the horrible dubbing Lee got may take you out of the movie.
That poster actually suggested the title translation should have been “Sister Was A Tramp”, lol.