Its 1360 and John Carpenter has started work on the new church spire in Chesterfield. He lodges with a widow, Martha, and strikes up a friendship with 12-year-old Walter and his older sister, Katherine. One morning he finds the body of the master builder in the tower. John is a suspect but the Coroner instructs him to find the murderer. Walter tries to help but disappears. A crowd gathers to watch the installation of the great windlass, a winding wheel, in the church tower. Has the boy found the murderer?