Reexamining the purported 1949 exorcism of a 13-year old boy in Mount Ranier, Maryland—the most famous and widely documented case in history—the author explores the subject of demonic possession in the light of science. Eyewitness accounts, unpublished photos and never before published documents from the archives of the Rhine Research Foundation provide fresh perspective on the events that inspired the novel, and later the film, The Exorcist.