The Nun (2018)

In 1952 Romania, two Roman Catholic nuns living at the Saint Cartha's monastery are attacked by an unseen evil force. The surviving nun, Sister Victoria, flees the attacker, a demon appearing as a nun, and hangs herself to avoid being used as a vessel by the demon. Her body is discovered by Frenchie, a villager who transports supplies to the nuns.

Upon learning of the incident, The Vatican sends Father Burke with Sister Irene, a nun in her novitiate, to Romania to investigate. The pair meet Frenchie and travel to the abbey, where they examine Victoria's body and take a key from her corpse. They then meet the Abbess, who informs them that because the nuns observe silence during the night, they must return the next day. Frenchie decides to leave the convent while Father Burke and Sister Irene stay behind. As Frenchie is leaving, he is attacked by a demonic entity in the form of Sister Victoria's corpse. Later that night, Burke is rescued by Irene after being lured by hallucinations of a boy he failed to save after a botched exorcism and is buried alive in the graveyard by the demonic entity.

Irene and Burke return to the abbey the next day, but only Irene can enter, as it is cloistered. She meets the other nuns and learns that they pray constantly, swapping shifts, to keep the entity at bay. The abbey was built in the Dark Ages as a castle for the Duke of St. Carta, an influential aristocrat obsessed with the occult. The duke summoned the demon through a rift in the catacombs but was killed by Christian knights, who sealed the rift with a vial filled with the Blood of Christ and reclaimed the abbey to contain the evil. But the bombings during World War II reopened the rift, unleashing the entity. Through a book he saw and took after being buried alive, Burke identifies the demon as Valak and discovers the Abbess has been dead all along.

Valak attacks Irene, who joins the nuns in prayer to ward it off. When she reunites with Burke and Frenchie, she discovers that none of the nuns she saw and talked to were real, and she had been praying alone. Sister Victoria had been the last nun in that abbey and had sacrificed herself to stop Valak from possessing her.

Theorizing that Valak can only be stopped if they seal the rift again with the blood of Christ from the reliquary, as the knights did, the trio retrieves the vial with Victoria's key. Irene asks Burke to elevate her status to a professed nun, which he does. In the tunnel, she is possessed by Valak, but Frenchie smears the blood of Christ on her face, casting out the demon. Valak starts to drown her in a flooded chamber. Irene, who had kept some of Christ's blood from the vial in her mouth, spits it into the demon's face, banishing it as the rift is sealed. Frenchie resuscitates Irene and reveals his real name is Maurice. Unbeknownst to the others, Valak possessed Maurice during the attack.

Twenty years later, at a university seminar in Wakefield, Massachusetts, Carolyn Perron watches as Ed and Lorraine Warren present footage of their attempt to exorcise a possessed older Maurice. Maurice grabs Lorraine, showing her a vision of Ed dying, which initiates the Warrens' investigation of the Perron farmhouse haunting.