NOTE: This spoiler was submitted by Jeremy

Tarascon, France, 1956 – A young boy named Jacques (Maxime Elias-Menet) arrives at a church to meet with Father Noiret (Pascal Aubert) for their daily chores. As Jacques goes to the lower level of the church, he hears a noise before a glass breaks violently. He gets Noiret, and they walk toward the altar where Noiret is suddenly flung up into the air and set on fire. Jacques flees the scene before the spirit of Valak (Bonnie Aarons) descends.

In Italy, Sister Irene (Taissa Farmiga) is now part of a new coven after her last experience with Valak. She has befriended a younger nun, Sister Debra (Storm Reid), who has a habit of going against the rules of the elders. Irene hears one of the other nuns tell the younger sisters about her experience with Valak, though the elder nun never mentions Irene by name.

Elsewhere in France, Maurice/”Frenchie” (Jonas Bloquet) works at a boarding school. He has a friendship with the schoolteacher, Kate (Anna Popplewell), as well as a good relationship with Kate’s daughter, Sophie (Katelyn Rose Downey). Sophie gets picked on by the other girls at the school, and Maurice frequently steps in to defend her. The school is run by the strict Madame Laurent (Suzanne Bertish), described as a hard woman who also mourns the death of her son Cedric.

In a nearby town, a child making deliveries ends up alone and is stalked by a demonic presence. Valak appears and holds the child up by the neck before snapping it.

Irene has a dream that she is following Maurice down an alley, where he appears demonic and possessed, calling to her for help. Afterwards, Irene is summoned to meet with Cardinal Conroy (David Horovitch) and other church elders. She is told about the death of Father Noiret, along with several other church officials have been found dead under mysterious and horrifying circumstances. Irene realizes Valak has returned, but when she is asked to investigate, she initially refuses. When she asks about Father Burke, Irene is told that he has passed away from cholera. Irene decides to go and is accompanied by Debra, who explains her own agenda for wanting to help (she lost her mother in a fire committed by racists).

At the school, Sophie is approached by the mean girls from before, who appear apologetic and invite her to play a game. They bring her up to a closed-off chapel in the school, where they challenge her to look at the window with a mosaic of a goat, saying that if Sophie looks away, the devil will come for her. The sun shines through the mosaic and makes the goat’s eyes appear red. The girls lock Sophie in there as she tries to get out, and she briefly sees a vision of Valak. Maurice opens the door and lets her out before scolding the other girls and leaving Sophie with Kate.

Irene and Debra arrive in Tarascon. Irene finds Jacques and tries to ask him about what he saw when Noiret was killed, as he simply took a rosary off him because he was scared. Jacques then disappears into a crowd with other boys playing in the streets. The nuns then go to the church and speak to a member that suggests Valak has returned after marking Maurice during his attempt to rescue Irene.

The nuns continue their investigation by traveling to Avignon and visiting the Palais des Papes, where they speak to a librarian about Valak. Irene and Debra learn that Valak is after an artifact referred to as “The Eyes”, for they belonged to St. Lucy, the martyr who would not die after she was set on fire. The librarian believes that the victims were descendants of Lucy, and the Eyes were last seen in a monastery which is now the boarding school.

During a night on the streets, Irene passes by a newsstand where the magazines and newspapers all flip their pages by themselves to create an image resembling Valak. As Irene approaches it, the lights flicker on and off until Valak appears and attacks her, causing her to lose consciousness. Debra finds Irene and gets her medical help. After she wakes up, Irene privately talks to Debra about her own mother, sharing the little memories she had with her before she died.

Back at the school, Sophie begins to notice strange things happening with Maurice, and he also feels the demonic presence surrounding him. Meanwhile, Madame Laurent is by herself in the chapel to investigate after learning Sophie was there and claimed to have seen something. She sees what appears to be Cedric running around, calling out to her. Valak lures her into a trap and kills her.

Irene and Debra go to the school where they locate the Eyes. Valak begins to wreak havoc with the possessed Frenchie, as well as summoning a demon goat to attack the girls. Debra and Kate end up in the care of the larger group of girls while Irene protects Sophie. The goat chases after the girls and takes the form of a dead Madame Laurent to terrorize them. After attempting to seal the goat off, it impales one of the mean girls through her shoulder before Debra tries to help her. In the ensuing chaos, the bell tower of the school collapses, but none of the girls are hurt.

Irene comes across Maurice, whose possession has now gone far enough for Valak to try and take over. Irene tries to use the Eyes to exorcise Maurice, with Debra arriving to help Irene. It appears to start killing Maurice, and he stops moving. Irene starts to mourn her friend, but he springs back to life with Valak using him to grab the Eyes and emerge in his true demon nun form. The demon starts to try and set Irene on fire, but it turns out she is a descendant of St. Lucy and her fire goes out. With help from Debra, they pray hard enough to save Maurice and also cause the wine in the room to turn into the blood of Christ. The barrels explode and drench Valak, sending the demon back to Hell.

Maurice recovers and reunites with Kate and Sophie. While Irene is happy to see her friend again, as is Maurice, she looks at him with worry in her eyes.

During the credits, Ed and Lorraine Warren (Patrick Wilson and Vera Farmiga) receive a call from Father Gordon about one of Valak’s hauntings.

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Valak returns to Earth because he marked Maurice ("Frenchie") when he saved Sister Irene after their last encounter with the demon. The evil nun starts to kill descendants of the martyr St. Lucy and is seeking a relic containing her eyes, as she did not die after catching fire.

Sister Irene and her new friend Sister Debra investigate the killings and find that the relic is at a boarding school where Frenchie now works. He experiences hauntings, and Valak attacks the girls at the school after the nuns find the relic. After sending a demon goat after the girls, Irene and Debra face off against Valak after he uses Maurice to get the relic and emerge to power. The nuns use their prayers to turn barrels of wine into Christ's blood to douse Valak and send him back to Hell.

Maurice recovers, but he is still doomed to be possessed before the Warrens eventually try to help him.