This film could be considered either a early giallo (like "Blood and Black Lace") or an Italian version of a German krimi (like "Dead Eyes of London"). A maniac is stalking the canals of Venice. Dressed as a frogman he is snatching young girls and taking them back to his lair, an underground monastery, where he ,uh, well embalms them as a way of preserving their beauty for all eternity.
This movie obviously makes very little sense--there has got to be an easier way to procure victims than donning a scuba outfit and pulling them out of gondolas, and for some reason the character dresses up in a robe and skeleton mask like the Phantom of the Opera even when he is alone in his hideout. Still as completely improbable as this is, it makes for some great scenes with pretty girls being dragged into canals at night by the sinister frogman (an idea later borrowed for the more violent Dutch thriller "Amsterdamned"), and the exciting finale where the masked killer hides among the skeletal corpses of monks in order to surprise the female protagonist who has wandered into his lair.
The movie is unusually depraved (always a plus) for a film made in 1965 with the whole embalming idea, and it breaks any number of cinematic rules. The cops are completely useless, chalking up the disappearances to accidental drownings, so it's up to an intrepid journalist and two hilarious winos who keep seeing "a big fish with a headlight" swimming under the bridge where they drink to crack the case. The end where the journalist hero rushes to save his girlfriend from the killer has some very unusual and shocking surprises. Of course, this movie doesn't offer the nudity or violence many Italian exploitation connoisseurs might expect (and it's in black and white), but it's still a worthwhile little film.