Evil is an important motif in this story and it underscores the theme of losing oneself as one grows up. The title comes from Macbeth. This is what the 3 witches say when they see Macbeth approaching them in the woods: "Something wicked this way comes" - i.e. "Something evil is coming our way." The "something evil" in this story is the Pandemonium Shadow Show. The characters that are associated with the show, then, all have names symbolic of evil and darkness: Mr. Dark, Mr. Fury, Dust Witch, Mr. Cooger (a cougar is a fearful animal that hunts in the dark). The only "good guy" in this novel (other than the two boys) is named Mr. Halloway. The word "hallow" means holy, and Mr. Halloway is able to save the boys in the end.