During the summer before sixth grade, Ethan Hinsdale and Gavin Porter planned to build a treehouse but unknowingly chose an ancient Native American Mound as their site. Three years later, Ethan and his friend Rachel seek guidance from Chogan, an elderly Cherokee, while searching for a missing prize-winning sheep. Chogan warns them that the Mound, over a thousand years old, holds mysterious powers and must be treated with respect.