It is about two 13-year-old best friends, Jim Nightshade and William Halloway, and their nightmarish experience with a traveling carnival that comes to their Midwestern home, Green Town, Illinois, on October 24. In dealing with the creepy figures of this carnival, the boys learn how to combat fear. The carnival's leader is the mysterious "Mr. Dark", who seemingly wields the power to grant the townspeople's secret desires. In reality, Dark is a malevolent being who, like the carnival, lives off the life force of those it enslaves. Mr. Dark's presence is countered by that of Will's father, Charles Halloway, the janitor of the town library, who harbors his own secret fear of growing older because he feels he is too old to be Will's father.