The son of an enslaved blacksmith learns that his father is using the rhythm of his hammering to communicate with travelers on the Underground Railroad.

When Pa falls ill, it's up to his son to help others along the journey-and also lead his family's escape.

Pa works hard as a blacksmith. But he's got another important job to do as well: using his anvil to pound out the traveling rhythm-a message to travelers on the Underground Railroad. His son wants to help, but Pa keeps putting him off. Then one day, Pa falls ill, and the boy has to take over.