Honestly I don't think this movie was meant to be taken seriously.
I think it was made to bring together 4 of the old great horror actors: Christopher Lee, Peter Cushing, John Carradine, and Vincent Price one last time. Lee is the only actor of the four still living. There are moments in this film that seem as though the actors are pulling our collective leg and inviting us to laugh along with them, e.g. when Victoria is found dead with her throat cut, and one of them (indicating the cause of death) says, "Piano wire." and Vincent Price responds, "He must have heard her singing." as she did earlier in the evening.
I could be a morning person if morning happened at noon.