This is a very weird film. It begins with an over-long, dialogueless scene in a laboratory where oddly-masked experimenters (the masks appear to be pillow cases) draw a blood sample from the arm of a seemingly cooperative female vampire. The vampire is naked, for no obvious reason other than the actress looks good that way. Nudity was often its own justification in early 1970s cinema.
As it is, there is almost no full nudity in this film. The vampire (Caroline Cartier) mostly wears a diaphanous orange wrapper that shows off her body, but still keeps her covered. A number of other actresses appear topless, sometimes with pasties. A set of twins (Catherine and Marie-Pierre Castel) spend a good bit of time in skirts that resemble Roman military kilts and tops made of loosely strung squares of translucent celluloid.
The plot, such as it is, involves a suicide cult whose members gather in secret and are randomly chosen to shoot themselves in the head, after which the vampire drinks the blood, “scientists” trying to figure out the secret of vampiric immortality, and a band of apparently trans-dimensional mutants who eventually explain everything.
It’s interesting, in a strange sort of way, once you get past the first fifteen minutes or so, which I suspect were intended to be artistic, but are mostly just boring. Rollin has definitely done better.