Exorcist II: The Heretic (1977)

Owing to his experience with exorcisms, Father Lamont (Richard Burton) is chosen by his superiors to investigate the death of Father Merrin (Max von Sydow), who died during the exorcism of young Regan MacNeil (Linda Blair). Lamont finds Regan under the psychiatric care of Dr. Tuskin (Louise Fletcher). By hypnotizing the girl, he is able to learn that Merrin previously exorcised the same demon from a boy in Africa. Hoping for answers, Lamont travels to Africa in search of the youth.