1950s British horror directed by Henry Cass. In the late 19th century, the anaemic Dr Callistratus (Donald Wolfit) is the governor of a brutal penal institution in a remote castle. Dr John Pierre (Vincent Ball) is wrongly convicted of malpractice and given a life sentence, but is soon employed by Callistratus to help him with his research. In a laboratory beneath the castle, Callistratus and his hunchbacked assistant Carl (Victor Maddern) submit inmates and young women to cruel experiments in blood transfusion. Outside the castle, Pierre's fiancée Madeleine (Barbara Shelley) determines to rescue him, but they both end up at Callistratus' mercy. The bloodthirsty doctor will stop at nothing to cure his debilitating condition, even if it means others must die so that he may live...