Thomas B. Allen's writings range from articles for National Geographic Magazine to books on American history. He has also appeared frequently on the History Channel as a participant in shows about war and espionage. He has lectured for the National Geographic on trips to the sites of historic events, such as Pearl Harbor and the D-Day beaches of Normandy. He was named by the U.S. Naval Institute as 2004 Naval History Author of the Year "for the sustained high quality of his literary contributions to Naval History magazine." His writing for National Geographic Magazine includes articles on Pearl Harbor, the Battle of Midway, the Eighth Air Force, and the sinking of the battleship Maine. Allen’s book Possessed revealed in detail the real exorcism that was the basis for the movie "The Exorcist." Possessed was adapted for a Showtime movie of the same name. He co-wrote the script for "In the Grip of Evil," a documentary based on the book.
In the first half, George Noory was joined by author Tom Allen who researched the real life case that the movie/book The Exorcist was based on.