In medieval England fallen under the shadow of the Black Death, a young monk called Osmund (Redmayne) is charged in leading a fearsome knight, Ulric (Sean Bean) and his group of mercenaries to a remote marsh. Their quest is to hunt down a necromancer - someone able to bring the dead back to life. Torn between his love of God and the love of a young woman, Osmund discovers the necromancer, a mysterious beauty called Langiva (Van Houten). After Langiva reveals her Satanic identity and offers Osmund his heart's desire, the horror of his real journey begins.