Heath Ledger stars as Alex Bernier, a young priest and protegee of the excommunicated head of a mysterious order known as the Carolingians, who has recently died under mysterious circumstances. Alex is sent by Father Driscoll to Rome to investigate the death; once there, he uncovers evidence pointing to the existence of a mysterious being known as a sin-eater, a being that exists outside the jurisdiction of the church and performs "last rites" on people who have been exiled by the Church. But as Bernier, aided by his old friend Father Thomas (Mark Addy) and an artist upon whom he once performed an exorcism (Shannyn Sossamon), gets closer to the sin-eater, he is besieged by doubt as to what it really is; human or beast, evil creature that preys upon humans or renegade angel who provides fallen sinners a last chance to make it into heaven.