Sure it doesn't make a lot of sense - it borrows heavily from "Carmilla" - but I think it was more of a calling card film for all involved behind the scenes. Besides Massacessi showing that he could be a director as well as a cinematographer, co-writer Claudio Bernabei was also the production designer (so a period piece would be the ideal genre to show off what he could do - he later directed a few of D'Amato's Filmirage productions), and the other co-writer Romano Scandariato later wrote EMANUELLE AND THE WHITE SLAVE TRADE for D'Amato and a Silvana Scandariato did costumes for a couple D'Amato productions while production manager Oscar Santaniello also worked on several of D'Amato's late seventies and early eighties pre-Filmirage productions. I think the film was mounted to show off their talents in other positions and Massacessi likely found several other people who he would end up working with over and over on later films.