Blood flows and thunder roars as Mary and Madelaine Collinson, attractive identical twins playing orphans, come to live with their witch-hunting, godfearing uncle (Peter Cushing), in the shadow of dreaded Karnstein Castle.One is good and timid while the other is bold and brazen. The latter cannot wait to find out more about the castle and the handsome young count (Damien Thomas). He is one of the undead and soon she is his victim. The question becomes, which twin is the vampire? John Hough has given Tudor Gates’ script [based on a characters created by J. Sheridan Le Fanu] a good pace and directed so that audiences can take it as straight horror or as a slight send-up. Settings, production values, camerawork and acting are all of a high standard.