A boy named Juan is witness, in the woods, of the assault of the band of Lorenzo el Quinto to a mysterious friar, who manages to escape after killing several of his attackers and takes refuge in the manor where the boy lives with his mother doña Carlota, a Countess, and her sister Beatriz. Basilisa, the servant of the house, conjures up Satan to free her son from an irreversible illness, but for that the evil must be transferred to an innocent soul, and she chooses Beatriz’s. The young woman then begins to be the victim of a possession, of which everyone blames the friar.