"The Demonologist: The Extraordinary Career of Ed and Lorraine Warren" is a nonfiction account of the life of two extraordinary human beings who have spent their lives battling the forces of evil, and assisting those who are threatened, attacked, or possessed by forces not of this world. The book is not only an encyclopedia of the supernatural, but is also a learning tool for those interested in spirits, both human and inhuman, as well as in the science and religion behind demonology. The Warrens present many stories of their own experiences with demons and ghosts, which help to explain their points about the dangers of the occult, and the supernatural as a whole, but also help to show the amazing power of the spirit realm, and the extreme consequences of accidentally allowing such forces into one's life.

The story, which is essentially a series of interviews with the Warrens, begins with a note from the author, Gerald Brittle, about how the book came into existence and how he is presenting the material. Next, a Foreword written by Reverend John Hughes, who notes the power of God and the dangers of Satan, and who promotes the sincerity and honesty of the Warrens.

In the next several chapters, discussions about previous experiences of the Warrens are given in context of explaining many issues surrounding demonology, such as differences in types of ghosts, how each of them came to be in the business, and how they typically conduct themselves when dealing with situations of hauntings. In the next few chapters, the Warrens tell of specific experiences with hauntings by ghosts, or those who have once lived. In the next sections, the couple turns to speak of demonic hauntings, or hauntings by demons who have never lived as human beings, but instead serve only Satan. They discuss each stage of a demonic haunting, ending with the stage of possession. The couple then discusses exorcism in terms of how it is done, variations on procedures, dangers, individuals involved, and outcomes of the process. Finally, the Warrens issue warnings to individuals to stay away from the dark path, and to remain positive and have faith, so that they can remain free from the torment of demons.

The book, focusing primarily on demonic possession, is an interesting tale of the journey of two individuals as they attempt to help those who believe they are being attacked by demons or ghosts. While there is definitely a religious slant to the book, one can expect nothing less from a couple who firmly believes in demonic possession and the power of God and of faith. At the same time, the book does present information that is useful, informative, and entertaining for even the non-religious person.