This book relates the true stories of five exorcisms performed in the 70s. The stories are told in a fictional format with lots of detail. It's a fast read, but I had to stop halfway through and take a break, since the incidents were disturbing and a bit vulgar at times. In addition to detailing the history of the possessed and how they opened their hearts to the demonic, the book gives the history of each of the priests who did the exorcisms. It's chilling, but the good wins out in the end, though not without a struggle.
You can see the books I've read so far (starting in 2011) here.