Protagonist Sigmund is elated to find that his sister Erika shares his same perverse and sadistic passions. However, after she ends up murdering a woman, Erika begins to have nightmares where she is haunted by the ghost of the victim. The dreams are so frightening, in fact, that it drives her to change her ways. She decides that she will become a nun, and live the rest of her life atoning for her wicked deeds.
Erika specifically wishes to go to a convent located in Ulm, but Sigmund - wanting his old, degenerate sister back - instead leads her to a monastery led by the abbess. Having conspired with the brother beforehand, the abbess exposes Erika to several perverse spectacles, in hopes of reigniting the girl's zest for sin. When this fails, however, the abbess restrains and sexually assaults Erika.
When Sigmund finally returns and finds that zero progress has been made, he takes matters into his own hands. In the dungeon, the abbess pleasures herself to the sight of the man whipping his sister. Eventually, a poor minstrel who is smitten with Erika, shows up at the monastery posing as a "friar" needing a place to stay for the night. Not wanting the stranger snooping around her domain, the abbess offers him soup which has been drugged with a sleeping agent. Anticipating that this might be the case, the minstrel only pretends to consume it, and later, manages to rescue Erika. The two then set fire to the monastery. The flames spread quickly, but it is not known if the abbess survives or not.