After one of the most baffling and disjointed pre-credits sequences in history, we follow Elizabeth Balljanon (?) as she returns to her deceased uncle's castle for the reading of his will. Her fiancé Jack (the word's worst reporter) accompanies her, and they're joined by two friends who presumably had an offscreen disagreement with either the lead characters or the producers, as they barely appear in the film. Elizabeth, who was extremely close to her uncle, inherits the entire estate. The Governess, Carol, insists that Balljanon had been planning to sell the castle to a neighbour. She then spends the rest of the film casually discussing the castle's history of murder and hauntings, which is in no way intended to convince Elizabeth to sell up. As the murders kind-of pile up (there's a body count of two before the climax), a local girl starts snooping around the castle, and Elizabeth's fiancé finally begins to believe her claims that she's the victim of a dastardly scheme to purchase her property at slightly below-market-value rates.
As far as I can ascertain, that is indeed the motive which drives the murderer(s). Given her impending nuptials, her fiance would presumably stand to inherit the property if she went completely loco and/or died, although it's unclear whether the murderer has the financial resources to actually purchase the property. There are ample opportunities to just do away with Elizabeth, and before she's married too, which would probably preclude the fiance from having a claim on the castle, but the aim seems merely to bump off characters of less consequence, and scare her up a bit.
But anyway. As I said, the film contains a lengthy checklist of ingredients from both gothic films and gialli, but the resulting broth is exceedingly mild. There's nudity, albeit mostly artfully framed or covered with strategically-placed limbs. There's a black-gloved killer, albeit one who kills two people. Two people are killed, albeit off-screen. There's a torture sequence, albeit one which involves only tastefully-framed whipping. There's a twist ending involving an unmasking, albeit one which makes no sense.
To briefly consider this ending; it's not giving anything away to say that the aforementioned dastardly scheme is being driven by an established criminal, who has assumed a new identity. This criminal isn't working alone (you may have an inkling of who their partner is from the above synopsis [and that's not a spoiler, the film makes it as blatant as I did]), but even so, he doesn't seem to be very good at crime.
One murder in particular, which happens prior to the beginning of the film (there are two such murders, which bump up the body count to four if you're feeling generous), leaves the door wide open for the later unmasking. The logic seems to have been that the murder in question will allow the criminal to assume the victim's identity and get close to Elizabeth. Given that his accomplice is already mighty close to her, though, this seems pointless. If the intention was to obscure the original identity (and face) of the criminal, the fact that they, at one stage, converse with an undercover police office using their original face (this'll make sense once you see the film) renders the identity-assumption utterly futile. And, while I'm on the subject, why didn't the police just arrest the criminal after that conversation, given the fact that they were on his tail? Clearly logic wasn't at the forefront of Ferruccio Casapinta's* thoughts when he was constructing the plot (which proved to be the only one he ever did construct); all he wanted was a twisty ending. On top of all that, the early shots of the criminal mastermind, which consist of identity-obscuring fleeting glimpses of his hair and body, clearly feature a double who doesn't really resemble the character he's supposed to be playing. This muddies the water to an unforgivable level when it comes to playing the accusation game.
On the whole, this is a basic pre-Argento inheritance-based plot which tries to use gothic iconography for extra thrills. It's still somewhat deficient on the thrill front, but it's probably not quite as bad as I've made out. It looks nice (even if the direction is pretty ropey), and gialli in castles are always worth a watch. If you like badly-choreographed fights, plots which don't stand up to scrutiny and beautiful sunsets, this may be a film you like a bit.