The events of the novel take place one October when Halloween comes early on the 24 and when both protagonists, James Nightshade and William Halloway, are almost 14 years old.

In a small town called Green Town, Illinois, a lightning rod salesman named Tom Fury approaches protagonists and next-door neighbors Jim and Will, who are lounging on their front lawn. The boys explain that Will was born one minute before midnight on October 30, while Jim was born one minute after midnight on Halloween. They say that they have no money to purchase a lightning rod, and the salesman gives them one for free. He claims a terrible storm is approaching, and lightning will strike one of their houses. Without the rod, he says, the house will burn. He touches both houses; his intuition prompts him to declare that the lightning will strike Jim’s house. Jim seems excited and unafraid of the coming storm. Eventually, Will persuades Jim to heed the salesman’s warning, and they put up the lightning rod together.

Jim and Will race each other to the local library where Will’s father, Charles, works as a janitor. Charles recommends some books to the boys. Jim chooses books about dinosaurs, and Will chooses The Mysterious Island by Jules Verne.