A nun committed suicide in a monastery far away in the Romanian countryside. For this reason, the Vatican appointed Father Burke (Demián Bichir) and trainee nun Irene (Taissa Farmiga) to investigate. After arriving at their destination, they first found the French youth Franche (Jonas Bloquet), who regularly delivered supplies to the monastery, and he was the first witness to discover the nun's body. The three entered the monastery, where the atmosphere was gloomy and ghostly, and the nuns were erratic, like ghosts. The abbess, whose face could not be seen, said that the nuns were praying silently and could only answer their questions the next day. In desperation, Father Burke and his party had to temporarily settle in the monastery. But as night fell, the real terror began to emerge, and the devil launched an indiscriminate sniping attack on the devout faith...