The Baron Janos makes love to a servant girl, while nearby a lady scientist wanders downstairs and reads up on werewolves. But is the thing that kills the servant girl, immediately after sex, a werewolf or something else? It's NSFW.
The 1970 horror movie Scream Of The Demon Lover is one of the silliest "throw shit at the wall and see what sticks" movies of all time, but it does sort of have a plot. It transpires that Janos, the Baron, isn't really turning into a werewolf at all - it's the Baron's brother, Igor, whom everybody thinks is dead but is actually a mad scientist who was horribly scarred in a lab accident. Igor is developing a secret formula that will regenerate his body, but meanwhile he has to kill every woman who makes love to Janos, because of his vociferous and bitter jealousy.
(And yes, that means that Janos has sex with the servant girl in the courtyard then just up and leaves her there as quickly as possible, so that Igor can surprise her the next time she opens her eyes. Despite this, Janos has no idea what's going on... What? It makes perfect sense!)
Mostly it's just more evidence of the incontrovertible law of horror films — you have sex, you die.