In 1971, Lucie Jurin escapes from a
slaughterhouse where she has been imprisoned and tortured for over a year. She is placed in an
orphanage, where she befriends Anna Assaoui. One day, Anna finds Lucie in a bathtub, her arm covered in cuts. Lucie begs Anna not to tell anyone. Anna embraces her, imploring her not to cut herself. Lucie responds that she did not do it. Later, Lucie is attacked by a disfigured, demonic woman. 15 years later, Lucie invades the home of a seemingly normal family, the Belfonds, whom she believes were involved in her torture as a child, and methodically kills each of them with a
shotgun. She calls Anna and gives her the house's address. While waiting for Anna to arrive, the demonic woman attacks Lucie, stabbing her hand and cutting her back. Lucie flees the house and encounters Anna, who tends to her injuries and enters the house despite Lucie's warning not to. Anna is horrified by the carnage, but decides to help Lucie clean the crime scene and dispose of the bodies. Anna kisses Lucie, who rebuffs her. Lucie is once again attacked by the woman and hides with Anna in a bedroom. Lucie recalls her escape, during which she ran from a pleading fellow prisoner who begged her for help. Anna discovers the Belfond mother is still alive and tries to help her escape, but Lucie catches them and beats the mother to death with a hammer. The demonic woman again attacks Lucie, but Anna only sees Lucie hurting herself; the woman resembles the victim that Lucie left behind at the slaughterhouse and is a psychological manifestation of Lucie's
guilt. Lucie then runs outside and kills herself by slitting her own throat. The following morning, Anna, while on the phone with her estranged, abusive mother, discovers a secret passageway in the home's living room, leading to a
subterranean chamber containing illuminated photographs of torture, and a living, brutalized, emaciated woman, proving Lucie's claims about the Belfonds. Anna attempts to help the woman, who is hysterical and nonverbal. She removes a steel blindfold that has been stapled to the woman's skull and helps bathe her, only to later find her mutilating her arm with a knife. A group of people arrives at the house, kills the woman, and captures Anna. The group's leader, identified only as Mademoiselle, explains that they belong to a
secret society seeking to uncover the secrets of the
afterlife by creating "
martyrs". They capture individuals and inflict on them systematic acts of torture, believing that their physical suffering will result in
transcendental insight into the world beyond. Though they have only produced "victims" who succumbed to the pain and were unable to speak, the group is determined to create martyrs who accept their suffering and report their visions of the afterlife. Anna becomes the group's newest subject. After a period of being brutally beaten and degraded, she is told that she has progressed further than any other subject and reached the "final stage", demonstrating her acceptance of her fate. She is surgically
flayed alive and reportedly enters an "
ecstatic" state. Mademoiselle arrives, eager to learn Anna's secrets, and Anna whispers into her ear. Members of the society gather at the house to pay
veneration to Anna for her martyrdom and hear Mademoiselle's announcement of the groundbreaking testimony. While waiting for Mademoiselle, who is in the bathroom, Étienne, an assistant, asks her from outside the door if what Anna said was clear. She unequivocally confirms and asks him in turn if he can imagine what comes after death. After he says no, Mademoiselle produces a handgun, tells him to "keep doubting," and shoots herself. An
intertitle explains that "martyr" is
Greek for "witness". The film ends with a shot of Anna lying
catatonic on a table, seemingly looking at something far away. During the credits, home movies of Anna and Lucie as children are shown. ==Cast==