Set in the year 1952 at the Carta Monastery in Romania, two nuns are going down to a dark hall toward a door that reads "God ends here". The older nun goes through the door to find some kind of artifact, while the younger nun, Sister Victoria (Charlotte Hope) starts to pray. The older nun emerges attacked and bloodied, telling Victoria to run before she is pulled back into the darkness. Victoria runs toward a window as the attacker while clutching a key, the demon nun Valak (Bonnie Aarons), moves slowly but closer toward her. Victoria asks God for forgiveness before she jumps and hangs herself. Sometime later, her decaying body is discovered by a man simply known as Frenchie (Jonas Bloquet).The officials at the Vatican learn of Victoria's suicide, which is considered the ultimate sin. They enlist Father Anthony Burke (Demian Bichir) to investigate. He seeks out a young novitiate named Sister Irene (Taissa Farmiga), who currently acts as a teacher to young girls. The two get together and go to find Frenchie so he can take them to where he found Victoria's body.The three go to the abbey where Frenchie leads Burke and Irene to the ice box where he left Victoria's body. Frenchie points out that Victoria is sitting up when he left her body lying down. Burke pries Victoria's fingers open and finds the key in her hand. They then take her body to give her a proper burial. While walking back toward the abbey, Burke notices fresh blood on the steps where Frenchie found Victoria's body. They then go into the chapel but cannot enter the abbey yet. They meet the Abbess (Gabrielle Downey), who informs them that are engaging in a vow of silence for Victoria, and that they may enter the next day.Burke and Irene go to their rooms while Frenchie leaves. He walks past the dark woods and sees what looks like Victoria walking through the woods. He follows her and ends up attacked by a demon nun. Frenchie picks up a cross from the ground and walks away with it.Irene tells Burke about a series of visions she experienced as a child, all of which ended with her hearing the phrase "Mary points the way". Burke then recalls an incident in France in which he was summoned to exorcise a young boy named Daniel (August Maturo) that had been possessed. Despite Burke's efforts, the boy sustained fatal injuries from the exorcism, and Burke has been wracked with guilt ever since.Later that night, Burke is awoken by the sound of music. He goes out into the woods and sees what looks like a demonic version of Daniel. The vision comes to life and pushes Burke into a coffin before an unholy force buries him alive, leaving him with a bell to ring. Irene also wakes up and wanders the chapel before she sees Valak in the mirror trying to attack her. She runs outside and hears Burke ringing the bell. Soon, multiple bells around graves start to ring, but Irene manages to find Burke's coffin and she starts to dig him up. Before she can reach him, demon hands start to pull at him, but Irene manages to free him. Inside the coffin, Burke then finds a bunch of books on the occult.The next day, Burke and Irene go to the abbey, but only Irene is allowed to enter. She meets Sister Oana (Ingrid Bisu), who tells her that the nuns change shifts to pray to keep evil at bay. Oana hears about Irene seeing Valak, and Oana explains the demon's origin. When the abbey was built during the Dark Ages, a duke obsessed with the powers of Hell tried to open a rift to summon Valak, but several men found and killed the duke before Valak could fully emerge, keeping him trapped using an artifact (the same one the nuns from before were looking for) containing the blood of Christ. He remained sealed in Hell until bombs from World War II dropped around the abbey and broke the rift open, setting the demon loose. Oana explains that Valak takes the form of a nun to look like the rest of them and prey on their weaknesses. Meanwhile, Burke reads about Valak and learns his name.Frenchie is in a tavern where he hears that one of the patrons had a 12-year-old daughter that committed suicide by hanging after allegedly seeing something horrible. After Frenchie tells the bartender that he went up with Burke and Irene to the abbey, the bartender warns Frenchie that the two of them may be the next victims.Burke once again attempts to enter the abbey, only to encounter the Abbess again to tell him he won't find another way in. He tries to ask the Abbess about the key that he found with Victoria, but she tells Burke it's too late and that Irene is lost. Her body then appears to go limp. Burke tries to lift her veil to see her, but her demonic body grabs at him until he rips her hand off of him.Irene awakens after seeing another frightening vision of Valak. She wanders outside her room and is once again attacked by the demon nun. Burke hears the noise and tries to save her but he is also attacked until Frenchie shows up with a shotgun. Irene finds the other nuns and starts to pray alongside them as an evil force carves a pentagram into her back. Irene then sees what looks like Oana's dead body, but she quickly realizes that Oana and the other nuns were not real, but visions.The three reunite as they realize that Victoria was not trying to commit suicide, but rather sacrifice herself so that Valak could not possess her body and spread terror. They head into the catacombs to find the artifact with Christ's blood. Irene realizes that "Mary points the way" is in reference to the statue of Mary that literally points the way to where they may find the artifact. Sure enough, they come across the vial containing the blood after opening its chamber using Victoria's key. Soon, Valak reemerges and attacks the trio. He starts to try and possess Irene while Burke is attacked by the demonic Daniel. Irene is briefly possessed, but Frenchie manages to throw some blood on her to free her. Valak unleashes a dark force upon Frenchie, and then tries to drown Irene. He pulls her up and sees that the vial is broken. She spits the blood in Valak's face, sending the demon back to Hell and sealing the rift.As the trio leave the abbey, Irene asks Frenchie his real name, and he says it's Maurice. We then see an upside down cross burned into the back of Maurice's neck.The film concludes with a clip from the first "Conjuring" movie in the present day where Carolyn Perron (Lili Taylor) is watching Ed and Lorraine Warren (Patrick Wilson and Vera Farmiga) give a seminar on their encounter with the possessed Maurice, who later committed suicide. His contact with Lorraine caused her to see visions, and unfortunately for her, it would not be the last time that she encountered Valak.