In The Light of the Demon, instances of demonic possession have increased in recent years, according to the Vatican. To help combat the growing number of cases, the Church decided to open a school aimed at training priests able to perform exorcisms. Sister Ann is among the students at the school, and, although she is one of the only women in the school, she believes her destiny is to perform exorcisms. When a teacher senses her special gift, he allows her to be the first nun to study and master the ritual. Her very soul will be in danger as the demonic forces she battles reveal a mysterious connection to her traumatic past.