Stephen Arrowsmith (Paul Muller), a scientist experimenting with the possibility of regenerating blood through electricity has his home and laboratory in the castle owned by his wife Muriel (Barbara Steele). Arrowsmith finds her later having sex with a gardener and disfigures him with a hot poker and burns Muriel's face with acid before electrocuting both of them. Arrowsmith hides their hearts in an urn and then uses their blood to rejuvenate the aged servant Solange (Helga Liné).
Later, Arrowsmith realizes that he is not Muriel's heir, but that the estate has been willed to her sister Jenny (Barbara Steele). Jenny is mentally unstable, and Arrowsmith marries her, later planning to have Solange drive her to the brink of sanity. Jenny begins having nightmares which include the sound of beating hearts and Muriel's voice urging her to murder Stephen. Arrowsmith brings Jenny to the doctor Derek Joyce (Marino Masé) who is convinced that supernatural forces are at work. Arrowsmith later tries to give Solange another blood transfusion, the doctor then discovers the hidden hearts of Muriel and the gardener. The two return as ghosts with Muriel burning Stephen alive while David reduces Solange to a skeleton by sucking her blood. The doctor and Jenny leave the castle and consign the two found hearts to a fire.