Like so many good things, the title of Bradbury's novel comes from Shakespeare. In Act 4, Scene 1 of Macbeth, one of the witches in the play exclaims:
By the pricking of my thumbs,
Something wicked this way comes.
Enter Macbeth, who has now been singled out as wicked. This couplet is referenced in Chapter 37 of the novel as the only explanation Charles Halloway can give to himself for his steadfast belief in the boys. In keeping with a theme developed through the novel, it is Charles's body that tells him something is wrong.
In this novel, the "something wicked" that comes to quiet Green Town, Illinois is a carnival of freaks. Its menacing nature is evident from their first arrival at three in the morning that sends the two boys Will and Jim into a frenzy of fear. Rather than see the carnival and its freaks as directly embodying evil, however, we would encourage you to think about how the carnival speaks to the dreams and temptations that exist in all our hearts. In other words, the carnival does not exist apart from human communities, but thrives on them. Its wickedness stems from its ability to twist dreams into nightmares.
We also feel obliged to mention the particular beauty and neatness of the lines form a poetic standpoint. The two lines are each seven syllables and follow a stressed/unstressed rhythm (otherwise known as a trochaic rhythm). This pattern is particularly ominous because of its heavy beat – you can think about footsteps coming to get you in the night. (Read more about this writing style in our guide to Macbeth.)This is in keeping with both the general style and tone of the novel – check out those discussions in this Shmoop guide for more.