A haunted cathedral. A possessed priest. Sarah Pearson and her team are sent on their first assignment together—to investigate a case of possession in Kutná Hora, Czech Republic. Father Hus, a respected priest, has reportedly succumbed to possession from a supernatural entity. On top of that, there are stories of a ghostly and bloody monk wandering the halls at night. As the investigation gets underway, it becomes clear there is more going on at the cathedral than they first thought. The team realise they are in a fight for their lives against a terrifying enemy with a plan that dates back centuries.