A deadly epidemic is spreading through the remote Cornish village of Clagmoor Heath. As darkness falls, it's victims are found foaming at the mouth with savage wounds on their necks. After his brother falls prey to the "black death," Harry Spalding (Ray Barrett, Terror From Under The House) travels with his new wife (Jennifer Daniel, The Kiss Of The Vampire) to Clagmoor to investigate his sibling's mysterious death. With little help from the unfriendly locals, Harry follows a trail of clues that leads him to the sinister Dr. Franklyn (Noel Willman, The Vengeance Of She), the doctor's strange, but beautiful daughter (Jacqueline Pearce, Doctor Who)... and a horrific family secret.