Plot
In the 13th century Villach, three women are accused by a priest of witchcraft, and are first hanged before being drowned. The priest performs a ritual on the three women using a book inscribed from the Key of Solomon so they can never return to life, but one of the women takes on a demonic appearance, sets the book on fire, and hangs the priest.
In the 14th century, German Teutonic Knights Sir Behmen von Bleibruck and Sir Felson join the Smyrniote crusades. After witnessing a civilian massacre during the capture of Smyrna, the two abandon their order and return to Austria.
Traveling through Styria, Behmen and Felson encounter people infected with the Black Death. They are trying to conceal their identities as deserters, but Behmen's sword crest exposes them. They are arrested and taken to Cardinal D'Ambroise, who is near death from the plague. The Cardinal asks the knights to escort an alleged witch who is suspected of causing the pestilence to a remote monastery where monks can perform a sacred ritual to cancel her powers and stop the plague. Behmen refuses, so D'Ambroise imprisons him and Felson, where they meet the alleged witch, Anna.
Both knights agree under the condition that she be given a fair trial and the charges of desertion against them be dropped. The Cardinal agrees, and they are accompanied by the priest Debelzaq, the altar boy Kay von Wollenbart, Johann, the captain of the Cardinal's Guard, and Hagamar, a well-traveled swindler who will serve as their guide in return for his pardon. Anna shows hatred towards Debelzaq while forming a connection with Behmen.
The group camps for the night, and when Johann decides to give up the mission and to convince the others to do the same, Anna attacks him, grabs his key to her cage, and escapes. The search for her leads the group to a mass grave, where Johann begins having visions of his dead daughter calling to him until he accidentally impales himself on Kay's drawn sword. When Anna is recaptured, she explains that she only ran away for fear of Debelzaq. They cross an old, crumbling suspension bridge, where Anna saves Kay from falling, grabbing him with unnatural strength. The group enters the dark forest, where Hagamar attempts to kill Anna, only to be stopped by the others. Anna appears to summon packs of wolves, which chase the group and kill Hagamar. An enraged Behmen tries to kill her, but is stopped by Debelzaq and Felson, who point to their destination on a nearby summit.
At the monastery, the men discover that all the monks have succumbed to the plague. They locate the ancient Book of Solomon, filled with the holy rituals used to defeat evil. Debelzaq begins speaking the ritual used on witches, just as Anna, in a demonic voice, begins recounting Behmen's horror at Crusader cruelties. Realizing that she is not a witch, but has been possessed by a demon, he frantically performs an exorcism. The demon possessing Anna melts the cage's metal and escapes while fighting off the knights. When Debelzaq throws a container of holy water on it, the demon flies away.
As the men search for it, they realize it is not trying to escape, but to destroy the book so that nothing can kill it. They find a room where the monks were making copies for others to use. The demon destroys the copies and possesses the dead monks to use as weapons. The three men fight the monks' possessed corpses, as Debelzaq continues the exorcism ritual. The demon snaps Debelzaq's neck and incinerates Felson. As Kay continues the ritual, weakening it, Behmen fights the demon and is mortally wounded. Kay finishes the exorcism ritual, and the demon is consumed by holy fire, and leaves Anna. Behmen asks Kay to keep Anna safe just before he dies. After their fallen friends are buried, Anna asks Kay to tell her about the men who saved her. They both leave the monastery, with the Book of Solomon safely in Kay's possession.
