The legendary Loreley has been living for centuries in a grotto beneath the river Rhein in Germany. Every night when the moon is full, she turns into a reptile-like creature craving for human blood. She needs to eat the hearts in order to prolong her own existence. Lorelei is attended by a servant named Alberic (Luis Barboo), and also has three maidens dressed in leopard skin bakinis. Two of these cavemwoman were credited as the popular Maria Luisa Tovar and Barbara Rey).
When one beautiful girl after another of a nearby boarding school is killed by her, a hunter named Sirgurd (Tony Kendall) is engaged to kill the monster. Sirgurd also falls in love with the beautiful teacher Elke (Silvia Tortosa).
Sirgurd then hears about the legend, and meets a mysterious woman introducing herself as Lorelei. For some reason he is not suspicious at all and falls for her trics. She wears a dark green fringed bikini throughout the movie.
Sirgurd stabs the loreley in monster form with a handy semi-magic dagger, which was made from Siegfried's sword. The monster turned into a pale Lorelei, who whispers, "we'll meet again in Valhalla" before dying. Her ghost then rides on a horse to gallop into the afterlife. When Sirgurd looks back he discovers that her body has turned into a skeleton.
- Helga Line appeared as Miss Eleonore, the Housekeeper in the 1963 Italian horror film, "The Blancheville Monster".
- Helga Line appeared as Taneal in the 1964 Peplum film, "Hercules and the Tyrants of Babylon".
- Helga Line appeared as Solange in the 1965 Italian horror film "Nightmare Castle".
- Helga Line appeared as Inge/Trude in the 1966 Italian crime film "Kriminal".
- Helga Line appeared as Marlene Schulman in the 1970 film, "Churchill's Leopards".
- Helga Line appeared as Matilde in the 1971 film, "Long Live Robin Hood".
- Helga Line appeared as Mabille De Lancre in the 1973 film, "Horror Rises from the Tomb".
- Helga Line appared as Zanufer in the 1975 Spanish horror film, "The Mummy's Revenge".