A bit about the movie....
For those of you who have not seen it, perhaps you should do that before you read any further.
Set in northern coastal Spain in the year 1546, this film takes some of the basic elements from the Edgar Allen Poe story and weaves them into a cohesive whole. It sets the stage after the Spanish Inquisition is over (although it was still on the books in Spain until the 1800's). This setting provides all that is necessary to make such an outlandish torture as a razor-sharp pendulum slowly descending seem plausible. (Did Poe come up with that idea? Or was it a known method of torture? I don't know.)
The story centers around Francis Barnard's (John Kerr) search for the truth to his sister Elizabeth Barnard Medina's (Barbara Steele) death. Vincent Price plays Nicholas Medina, who is Elizabeth's husband and son of the infamous Inquisitor, Sebastian Medina (also played by Price). Both Nicholas and his sister Catherine (Luana Anders) are staying at the Medina castle when Francis arrives.
There are various plot turns—music being played, a room being torn up, Elizabeth's tomb being opened—all of which were caused by Elizabeth herself. Unbeknownst to everyone but Nicholas' best friend, Dr. Charles Leon (Anthony Carbone), she is very much alive. She and the doctor have been plotting to get Nicholas' money. All her machinations are to drive her husband insane.
She succeeds brilliantly, but in a satisfying twist, Nicholas' insanity turns on her. He locks her in an iron maiden, believing he is his own father and she is his adulterous mother, Isabella. Dr. Leon is mistaken for Nicholas' uncle Bartolome (with whom Isabella had committed adultery), and after a brief struggle falls to his death in the pit. Unfortunate Francis arrives on the scene just in time to replace Dr. Leon, and is put through the ordeal under the pendulum.
This is a terrific scene. Price is at his best in this film when he's playing insane Nicholas. And it's obvious if you consider it, Nicholas was insane already. In an earlier part of the movie, when Catherine is taking Francis down to see where his sister is interred, there is a horrendous grinding mechanical sound coming from one room. We find out later that this is supposed to be the sound of the pendulum mechanism. Nicholas comes out of the room when Francis tries to investigate and claims only that he was maintaining some device. Why on earth would he keep the pendulum working—a device of torture—if he were not seriously unbalanced? Besides, the rest of the torture chamber is left unattended. (Note, however, that when the actual device is working to slowly kill Francis, you don't hear that horrible loud noise, so what was it Nicholas was doing? We assume the pendulum, and you DO here some of the same sounds, but they are not nearly as loud.)
Luckily for Francis, Catherine investigates the torture chamber and hears him call for help. She hears the sound of the pendulum mechanism as it starts and reacts visibly to it. She knows what it is and how it works. One must assume she knew her brother was maintaining this device, though she must have been in denial about his intentions.
Between her and the servant Maximilian, they free Francis. It is interesting to note that the part where Maximilian struggles to get the door to the pendulum room open has been cut from the film, but if you watch the trailer (on the DVD) you see a glimpse of that action.
Nicholas ends up along with Dr. Leon at the bottom of the pit. As the camera pans out, there is Elizabeth, a gag around her mouth, her hands clutching the edges of the small window of the iron maiden. This is a pretty big flaw, actually. If her hands were able to reach her mouth, why didn't she take the gag off and scream? I personally have always found it annoying in a movie when someone has a cloth gag around their mouth and then doesn't try to scream. Even if your mouth had been stuffed with another rag, you could still make some kind of sound. Same thing goes for Francis when he gets gagged by Nicholas.
Nonetheless, it's an effective ending. Elizabeth gets her just reward as Catherine claims that no one will ever enter this room again.
Naturally, I have left out a great deal. The atmospheric mood of the film was beautifully done. There is a suggested potential romance between Francis and Catherine. The flashbacks into the past as both Catherine and Nicholas tell of things that had happened were done with blue filters and some distortion, but were effective and contributed to the mood. And of course the splendid sets! All in all, a great piece of entertainment.
Of note on the DVD is the commentary by director Roger Corman. This was a fascinating glimpse into the making of the film and well worth a listen. When activated it plays out over the soundtrack as he comments on the action as it happens. Between that and the theatrical prologue, the DVD is a find.