The Secret of the Underground Room: A Johnny Dixon, Professer Childermass Book

Professor Childermass is stunned when Father Higgins claims that a ghost is trying to contact him. Then the priest disappears. When the professor and Johnny catch up to him, they make a terrifying discovery -- Father Higgins is possessed by Masterman, the spirit of a long-dead knight determined to rule the world. And it looks as if Masterman is going to get his way. "Has enough chills to satisfy readers not quite ready for Stephen King."-- School Library Journal