Genre-hopping journeyman Hough alighted at Hammer to finesse one of the studio’s most ingenious attention-getting gimmicks: the third part of the 19th-century-set Karnstein trilogy launched by The Vampire Lovers stars identical-twin Playboy Playmates Mary and Madeleine Collinson. One of the young ladies is lustily drawn into a vampire cult, while her sister remains pure of heart—but as the stakes rise their take-no-prisoners Puritan witch-hunting uncle Peter Cushing has a devil of a time figuring out which is which.