Blood suckers (1971)

A group of friends search for a young English Oxford student who has disappeared whilst researching in Greece. They are shocked to find that, wherever he has been, certain unsolved murders have taken place. Not believing that their friend could be the perpetrator of such acts, they press on with their search, finding him under the spell of a beautiful Vampire, whose blood-sucking methods include the use of sado-masochism. Believing they have killed her, the group return home, unaware that their friend is now a Vampire.