At the traveling carnival, the hunchback Dodger activates the Ferris wheel while Mr. Cooger rides it backward. As it runs in reverse, Mr. Cooger becomes younger and younger. As the Ferris wheel stops, Mr. Cooger steps off... transformed into a ten-year-old boy. He runs off to the home of an elderly widow, Mrs. Foley, as he has for the last several days. He's unaware that a local boy, Hank Walterson, has snuck out for the night and watched the entire thing.
Hank stays throughout the night and watches as Cooger returns just before sunrise, is restored to his normal age, and tells Dodger that he'll have to return to Mrs. Foley's later to complete their plan. Hank then goes to see his friend Peter and tells him to come to the carnival with him. They go to the carnival that night and watch as Cooger has Dodger use the Ferris wheel again to transform Cooger into a ten-year-old. They follow Cooger into town where he goes to Mrs. Foley's house again. Hank explains to Peter that two weeks ago when the carnival arrived, Mrs. Foley took in a young orphan boy, Joseph Pike. The boy is Cooger.
The two boys watch through the window as Mrs. Foley feeds "Joseph." It starts raining and Hank insists on warning Mrs. Foley that Mr. Cooger plans to steal her money right before the carnival leave. They knock on the door and Mrs. Foley lets them in. Hank tries to explain that the transformed Cooger plans to take her money and then revert to his normal page, and nobody will ever connect him to the boy who took her wealth. Mrs. Foley is understandably skeptical and tells them to leave, while Joseph watches. The boys walk down the sidewalk and turn to see Joseph looking at them from the window.
When he goes back home, Hank tries to explain to his parents what happened. They don't believe him and Mr. Walterson tells him to stay away from the carnival. In his room, Hank calls Peter and tells him that they have to move tonight before the carnival leaves. Mr. Walterson overhears him talking and takes his clothing and says that he's grounded.
At Mrs. Foley's house, Joseph waits until the widow dozes off and then starts searching the house for her jewels. He finds the money but Mrs. Foley wakes up and starts looking for him.
Outside, Peter goes to meet Hank at Mrs. Foley's house. Hank finally shows up, naked except for his sneakers. He borrows Peter's raincoat and they listen as Mrs. Foley searches for Joseph. When she finds him, Joseph throws a pillowcase over her head before she can see him and runs out. Mrs. Foley goes after him and sees Peter and Hank, and assumes that they're the thieves.
As Hank and Peter chase after Joseph, Mrs. Foley calls the police and then Hank's father to tell him what happened.
Joseph runs to the carnival and gets onto the Ferris wheel as the police sirens sound in the distance. He tells Dodger to start the wheel and it begins to run normally, making him an adult. As the police arrive with Hank's parents and Mrs. Foley, Hank throws himself at Dodger. The two of them fight and Dodger is knocked against the control lever. The Ferris wheel goes faster and faster as Cooger screams in pain and terror. Hank runs to his father and tells him that Mr. Cooger stole the jewels. Everyone turns to the wheel and stares as the Ferris wheel finally slows... and Cooger has become an ancient, decaying corpse.