The nun features the story of a youthful nun at a secluded convent in Romania who commits suicide. On the brink of her final vows, a novitiate alongside a priest with a spooky past are then tasked by the Vatican to conduct investigations. Jointly, they unearth the guild’s ungodly classified secrets, jeopardizing their lives, faith as well as their souls.
It starts off with two nuns going down to a dark hall towards a door emblazoned with the words “God ends Here”. The older nun goes through the door while the younger nun stays behind, praying. The older nun on returning is attacked and bloodied, telling Victoria, the younger nun, to run! On the run, Victoria jumps and hangs herself as Valak, the demon nun, while clutching a key is after her.
On the discovery of her body, Vatican officials then enlist Father Anthony and Sister Irene to investigate, alongside Frenchie, who had discovered Victoria’s body.
On arrival, Frenchie leads Anthony and Irene to the icebox where he had left Victoria’s body but to his surprise, the body is fitted up whilst he left her body lying down. On prying Victoria’s fingers open, he finds a key in her hand, and they decide to go and give Victoria a proper burial. However, Abbess informs them that they are engaging in a vow of silence of Victoria and they can’t access the abbey until the next day. Frenchie leaves as Anthony and Irene then go to their rooms. On his way, Frenchie is attacked by a demon nun resembling Victoria. Irene is also attacked by Valak while Anthony gets buried.
It ends when Anthony, Irene, and Victoria reunite as they realize that Victoria wasn’t trying to commit suicide but rather sacrifice herself so that Valak could not possess her body!