Father Lamont (Richard Burton) is sent by his Cardinal (Paul Henreid) to discover the death of Father Merrin (Max von Sydow) and also to see why Regan (Linda Blair) was possessed by the demon...

Father Lamont (Richard Burton) is sent by his Cardinal (Paul Henreid) to discover the death of Father Merrin (Max von Sydow) and also to see why Regan (Linda Blair) was possessed by the demon Pasuzu. Father Lamont travels around the globe to Africa in search of another possessed by the same demon named Kokumo (James Earl Jones) which Father Merrin had performed an exorcism several years in the past. Kokumo tells Father Lamont that the demon lives inside locusts who fly around the world. When Father Lamont returns to New York were Regan lives he discovers the demon has reached Regan through Dr. Gene Tuskin's (Louise Fletcher) hypnosis machine. Father Lamont travels to Regan's old home in Georgetown to defeat the demon. However this time the demon takes control of Regan, Father Lamont, and Sharon (Kitty Winn). Father Merrin's spirit returns to help.