A young girl, Helga (Rosalba Neri), with two girlfriends goes to the Hornbergs' castle, a sixteenth century mansion which, according to popular belief, is the devil's dwelling. During the visit she comes across a portrait of a woman who looks much like her. The girls ask for hospitality to the sinister mansion's guardian, and during the night Helga dreams and lives the horrible events that happened to her many centuries before, when she became the demon's lover…