Demons Square: Susan Garth is possessed, but how and to what purpose?
Susan Garth has been unable to attend mass for some time. Nausea overcomes her whenever she gets too close to the church. Her behavior has also been erratic, quarrelsome, and, at least once, obscene. Her father is dead set against a psychiatrist and so he asks the parish priest for help.
The priest is a recent transfer and has to battle with his modern sensibilities to believe in the evil that has taken over the girl. The page count is low, but the characters represent a neat cross-section of American Catholics in the early '60s. There was a lunatic pamphleteer, too, representing the very real prejudice Catholics still faced in that time.
I have not read 'The Exorcist', but many elements from the film version are present. Russell brings the devil in to modern times. Many have borrowed Russell's methods, but this still is genuinely scary.