This novel by William Peter Blatty set the bar high in horror books and horror films. The simple idea of a young girl becoming a slave to the dominion of a higher and evil power has become a trope in later horror stories. This is the one that is the bar.
Now, the premise is simple, as I have explained it already, but I must again say how simplicity makes a story better. The idea is simple, however, the way the story progresses is quite intricate. It goes from she is ill in the head to she is suffering from a form of psychopathy. Then, the story leads to getting a priest, who thinks she is suffering from a mental disorder, and then an exorcism.
The story never goes out and says, "She is possessed by a demon!" That would be too obvious, but the buildup to the inevitable ending is one of great talent that few authors can match.
As many know, this was later adapted into the Oscar-winning film version of the book, screenplay written by William Peter Blatty. The film is relatively close to the book in such an amazing level of detail, but there is something one gets from reading rather than watching.
Reading this book allows one to envision the story as one sees it, not necessarily the cinematic version. Reading the book allows one to appreciate this simple story of great detail and suspense in comparison to other horror stories.
Overall, this book is one of incredible storytelling and is worth a read by every literate person, not just horror fans.