Extracted from the Secret Police Archives of a European Capital is a long title for a movie, so let’s just go with Tragic Ceremony.
After sailing all day, Jane (Camille Keaton), Bill (Tony Isbert), Joe (Máximo Valverde) and Fred (Giovanni Petrucci) have run out of gas somewhere near that old Frankenstein place — no, but seriously, somewhere in England — and end up at the mansion of Lord and Lady Alexander (Luigi Pistilli, never to be trusted, and Luciana Paluzzi from A Black Veil for Lisa and The Green Slime) and are invited to stay.
That night, Jane interrupts the Satanic ceremony in the basement and gets saved by Joe, who stabbed Lady Alexander and the cultists all kill one another. This gets reported on the news like a Manson Family copycat murder and the evidence points to the four of them as the ones who did it.
Then, the movie shifts into slasher mode, as perhaps that’s not Jane at all. Perhaps.
Directed by Riccardo Freda (The Iguana with the Tongue of Fire) — maybe, Fillipo Walter Ratti has also been credited with some directing — and written by Mario Bianchi (he also wrote another movie that Freda directed, The Murder Secret).