This movie is actually a remake. It had been made before as Kagi (1959) about twenty-four years earlier and directed by respected Japanese director Kon Ichikawa. The movies are both adaptations of the 1956 Japanese novel "Kagi" by Jun'ichirô Tanizaki. "Kagi" has also been filmed a number of other times - See: Kagi (1974) and Kagi (1997) whilst another Japanese version, Kagi (1983), was also released in the same 1983 year as this movie. This picture is actually the third version of the book and was released before Kagi (1983).
The story's location was moved from Japan in Jun'ichirô Tanizaki's novel "Kagi" (which was also the location in the four Japanese versions of the book including Kagi (1959)) to Venice, Italy for this movie.
This movie was made about twenty-seven years after Jun'ichirô Tanizaki's novel "Kagi" was first published in 1956. The first filmed version of the novel, Kagi (1959), was made about three years after the book was first released whilst the second version, Kagi (1974) was made about eighteen years after.
Stefania Sandrelli once said of this movie: "I like to play all parts. If I have to be nude, I have to be nude. But I never have the impression of being naked on the set. Yes, I was a little afraid of this film at first. The script shocked me - and amused me because the subject is nothing but sex. Nothing else is discussed in the film."
Director Tinto Brass went to London to find a British actor to play the part of the husband, Nino Rolfe. Brass cast British actor Frank Finlay after seeing him play Antonio Salieri in Peter Hall's stage production of 'Amadeus' at the Her Majesty's Theatre in the West End.
'The Key' is one of the English titles of Kagi (1959), the first filmed version of the Japanese novel 'Kagi'. That movie is also known as 'Odd Obsession'. In Italy, it is also known as 'La Chiave', the same Italian title as for this movie.
This movie is set in the era of the approaching Second World War in Venice, Italy where there is a backdrop of fascism. Director Tinto Brass had previously helmed Salon Kitty (1976), a movie which was set in World War II amidst Nazism, i.e. German fascism.