When Tommy Fuller acts up in church, Reverend Morse stops the service and alerts Tommy’s father. Deacon Fuller sends his son home ahead of the family. He orders him to go straight to his room, but Tommy makes a stop in the barn to see the horses and jump in the hay wagon. He hears noises in the hay and discovers a family of runaway slaves.
The father of the family hiding introduces himself as Big Jeff. His wife is Vinnie, and she carries Baby Pearl. Their 9-year-old son, Little Jeff, is about Tommy’s age. From them, Tommy learns his own father is a conductor on the Underground Railroad, a person who helps runaway slaves escape to freedom. Little Jeff explains that he and his family must follow the drinking gourd, or the Big Dipper, in the night sky. This points them toward the North Star, which will show them the way to Canada.
Deacon Fuller arrives. He’s unhappy that Tommy has disobeyed his orders and discovered his secret, but now he swears the boy to secrecy as well. He and Tommy drive the wagon to the riverbank with Jeff and his family buried under the hay. While Deacon Fuller is looking for a hidden canoe, a U.S. Marshal and his men see Tommy and the wagon. They question him.
Tommy tells the men that he’s there at night because he’s running away from his father. The men, who witnessed Tommy’s antics in church that morning, laugh and let him go without searching the wagon. Once they’re gone, Deacon Fuller returns and takes the slaves across the river, and Tommy drives the wagon home.
When Deacon Fuller returns that night, he talks to Tommy about his reasons for helping slaves. He admits he and Tommy broke the law, but he says human beings shouldn’t be another man’s property. He says he will continue to fight against these unfair laws, and someday, they will be changed. Tommy looks out his window at the stars, thinking of his new friends and their journey to freedom.