Beatriz (1976)

In the woods, a boy named Juan witnesses the Lorenzo el Quinto's band's assault on 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--the Countess Doña Carlota--and her sister Beatriz. Basilisa, their servant, 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 becomes the victim of a possession, for which everyone blames the friar.—jsanchez