The titular hero (Janson) is a wandering ex-soldier, who hunts vampires 'cos they took his family, and slays them with the help of a hunchback professor (Cater) and a conveniently-passing babe (Munro). An old army buddy calls him in, as the village girls are having their life drained away. It's probably giving nothing away to mention the suspiciously-youthful local nobility. Clemens' sole feature, he's best known for hsi TV work, and there are distinct echoes here of the Clemens-produced New Avengers, with a trio of a wily veteran, a macho action guy and a sex-symbol, though Munro never does much beyond act as eye-candy and bait.
For a late Hammer, this is remarkably restrained, particularly sexually; it's painfully clear they were angling for a franchise, on TV or film. It also rewrites much accepted vampire lore: crosses have little effect, nor does daylight. Indeed, the best scene has our heroes trying various methods, in order to find out how to kill this particular species. There are a couple of other very cool elements - flowers wilt when the vampire passes, and time "stops" during an attack - though they mean nothing. Everyone plays it gratifyingly straight: Cater is a decent substitute for Peter Cushing in the expositional role, and check out Ian Hendry's cameo as a lecherous thug. But if anyone can explain the blind girl sitting in the background, I'd be very interested to hear from them.