This theme frames the central issues of the book and is raised directly in the title. Something Wicked This Way Comes implies that evil is descending upon an otherwise good town. Evil is sensed clearly throughout the novel (see "Fear"). Evil is moreover given a physical form in shape of a carnival and its freaks. In order for evil to have any power at all in the novel, though, it has to be believed. By the end of the novel, however, we question the extent to which evils, such as the carnival, are products of our own human natures – namely, our tendency to succumb to temptation.
Weapons on the side of Good in Something Wicked This Way Comes include love, laughter, and friendship. This is not new in the world of fantasy literature. Lord of the Rings, for instance, and The Lion, the Witch, and the Wardrobe both depict worlds where Good stems from these pure human emotions that cannot be touched by evil. (Harry Potter would be a more contemporary example.) This pure view of good and evil lends itself well to young adults.
In Something Wicked This Way Comes, evil is substantiated purely through physical reaction and not so much the antagonists' actions.
Boyhood and youth in Something Wicked This Way Comes are upheld as the ultimate good.