When I was 12 the movie "The Exorcist" came out, a book version of the story appeared around the same time, as did the Mad Magazine satire titled "The Ecchorist". I somehow got a copy of the book, but got scared because I was reading it on the school bus, threw up, and thought the demonology in the book made me throw up. I mention this because "Possessed" is the "true" story of the exorcism which inspired that book and movie.
Possessed: The True Story of the Most Famous Exorcism of Modern Time: This book concerns troubles faced by a family in a small town outside Washington DC. They were a good Lutheran family of German descent, and had an eccentric Aunt who visited them regularly. The Aunt believed in Spiritualism, a "church" that practiced ways of contacting spirits. While most of Christianity sees attempts at contacting spirits to be "an abomination unto the Lord (as it says in Deuteronomy), the Spiritualists believe it is safe and natural.
This Aunt introduced a young boy in the family to the use of the Ouija board. The Ouija board nowadays is presented as a childs playtoy, and involves a "planchette" (pointer) that people put their hands on. The planchette is moved across a board which has letters and numbers, and the idea is for spirits to connect with the hands of the Ouija board user, having the spirit move the planchette across the board, and to recieve messages from beyond.
After the Aunt's death, the boy spent a lot of time with the Ouija board, presumably attempting to contact his Aunt. Shortly after strange things began happening in the house at night, and not just their own house but everywhere the young boy went. These included objects levitating, beds or mattresses shaking, scratching sounds, and more. The book makes this seem like a horror movie come alive.
At the beginning the family simply thought the scratching sound meant a rat was trapped under the floorboards. But after awhile they were disabused of that notion as the events became more dramatic, and would occur in other places.
Eventually the family contacted priests, first of their Lutheran faith. The book goes to great length to discuss the different views of the religions on such "Medieval" concepts as Possession by the Devil. Protestant churches such as the Lutherans discarded such superstitious notions, and so the Lutheran priests they consulted were of little use, and referred the family to the Catholics.
The book describes the ordeal of the first Catholic priest they consulted. Unfortunately the records are locked up in the Archdiocese of Washington, but it appears the priest admitted the young boy to the Georgetown University Hospital to perform an exorcism. Somehow the young boy was able to work his hand free, and use part of the bedsprings to slash the priest so badly he required 100 stitches in his arm. That exorcism attempt ended almost immediately.
The family eventually went to St. Louis where most of their family resided. They then contacted Jesuit priests with St. Louis University, and that led to another Exorcism, this time with more experienced priests than the first one.
Consider the plight of these priests living in a modern age. The events in the book occurred in the Winter and Spring of 1949, the modern technological marvels of our current age were just beginning to bloom. And, in the midst of that, these priests were facing an ancient phenomenon which modern science would say cannot exist.
They knew they could ignore the problem. If they did, the family would either go to a different disoscese, one more amenable to performing exorcism, or else the young boy would end up in a mental hospital. Which just leads me to question, how many of the mental hospital patients are really suffering from spiritual problems, but the modern science under which mental hospitals operate cannot admit that spiritual problems even exist, much less know how to treat them?
Ultimately these priests chose that their fundamental work is the "advancement of good, and the defeat of evil" and so went forward with the exorcism.
Along the way of telling the story, the author intersperses quite a bit of details about the Catholic Church, the Jesuit order, and various bits of previous exorcisms. The book is a wonderful story-telling, that also serves to educate about the history of exorcism.