Everything you need to understand or teach Legion by William Peter Blatty.
Legion opens with police lieutenant William Kinderman meditating upon evil in the world, then flexing to consider the good, in one smooth motion. The setting is soon revealed as that of a particularly horrible murder, the first in a series; but throughout the scene—and the novel as a whole—Kinderman's ruminations alter nate with, and are given at least as much weight as, the homicide investigations. "It seems to me...