Peter Beaupre is the leader of a group of thieves who have stolen a valuable Air Force computer chip. When a bag mixup at the O'Hare Grouchy old Mrs. Hess accidentally brings home from the airport a toy remote-control car with a top-secret microchip hidden inside. Beaupre and his followers: Alice Ribbons, Earl Unger, and Burton Jernigan, start searching Mrs. Hess's neighborhood and breaking into houses searching for the chip. 8-year-old Alex Pruitt reports seeing Beaupre and his followers, but Alex's sister Molly, his brother Stan, and his parents Jack and Karen refuse to believe him. Beaupre and his followers figure out that the chip is in the Pruitt home, because Mrs. Hess gave Alex the remote-control car. Alex is left home alone with chickenpox when Karen goes to work, Jack goes out of town on a business trip, and Molly and Stan go to school. When Beaupre and his followers break into the Pruitt house, Alex is ready with some of the most painful booby traps Beaupre's gang will ever face.