Brother and sister, Casey and Kiley, go back in time again with their alien friend Tuttle. In this adventure, they travel to Weaverville, a famous mining town in Northern California, during the 1850s. The Gold Rush era comes alive as the children encounter wild animals, stagecoach robbers, miners, kidnappers, and something dangerous protecting a mine. Casey and Kiley work together with two pioneer girls, the Sheriff, his deputies, and a grizzled fur trapper to help find a missing young boy who the Weaverville townspeople say was taken by Bigfoot. Can they find him?