A young boy Hee-Joon is possessed by an evil spirit. Nun Yunia tries to save him, assisted by Nun Mikaela. Priest Paul attempts medical treatment, while Priest Andrew performs an exorcism to rid Hee-Joon of the spirit.
A boy named Hee-Joon (Moon Woo-Jin) becomes possessed by an evil spirit. People around him struggle to save him. Nun Yunia (Song Hye-Kyo) takes action to save the boy, who is overwhelmed by powerful pain and she never gives up on the boy. Nun Mikaela (Jeon Yeo-Bin) takes an interest in Nun Yunia's actions and decides to help her even though everything is in chaos around them. Priest Paul (Lee Jin-Uk), who is also a psychiatrist, believes that he can cure Hee-Joon with medical treatments. Priest Andrew (Heo Jun-Ho) performs an exorcism to expunge the evil spirit from the boy Hee-Joon. — Asian Wiki