The film begins with a young girl, Lucie, as she escapes from a disused abattoir where she has been imprisoned and physically abused for a lengthy period of time. She is then placed in an orphanage, where she is befriended by a young girl named Anna. Anna soon discovers that Lucie is constantly being attacked by a ghoulish "creature."



Fifteen years later, Lucie bursts into a seemingly normal family's home and kills them all, claiming that the two adults of the family were the ones responsible for her childhood trauma. She is periodically attacked by the "creature."



Lucie calls Anna, who comes to the house to help her bury the bodies. Anna discovers the mother is still living and tries to help her escape, but is discovered by Lucie who kills the woman. Having realized her vengeance, the "creature" - in actuality, a psychological manifestation of Lucie's guilt over not being able to save another girl who was also imprisoned and tortured with her all those years ago - drives Lucie to kill herself. As Anna is clearing up the house, she discovers a secret underground chamber and imprisoned within is a horribly tortured woman. While Anna attempts to care for her, strangers arrive and shoot the woman dead.



Captured by the menacing newcomers, Anna meets their leader, an elderly lady only referred to as Mademoiselle. She explains that she belongs to a secret society seeking to discover the secrets of the afterlife through the creation of "martyrs." Systematic acts of torture are inflicted upon young women in the the baseless belief that the extreme pain will result in a transcendental insight into the world beyond this one.



Anna is imprisoned in the chamber and becomes their latest subject. After an unspecified period, during which she is repeatedly beaten and tortured, she is told she has reached the "final stage," where she is then flayed alive. Anna survives the procedure, entering a state that is summarised to be 'euphoric' and likened to achieving transcendence. Mademoiselle arrives to bear witness to her description of the afterlife.



A group of people visit the house to celebrate the successful martyrdom. As they wait downstairs to learn of Anna's words and insight Mademoiselle is upstairs in the bathroom. Through the closed door she asks another member, "What do you think comes after death?" He replies that he does not know and she in turn replies, "Then keep doubting" and shoots herself. An intertitle informs us that "martyr" is the Greek word for "witness."