Their magic tree house takes Jack and Annie back to the Wild West, where they experience excitement and danger and try to solve a riddle.

In 1851 twelve-year-old Sarah is a free Black, happy living with her parents, grandparents, and brother on their own farm in Iowa; but her father has been bitten by the gold bug and wants to take the trail west to California, and after some argument it is decided that the grandparents will stay on the farm, but the rest of the family will go; the journey will be difficult and dangerous, but if they survive extreme weather, difficult terrain, illness,...

Traveling with his owners from Missouri to Oregon in 1848, Koda, an energetic two-year-old quarter horse, finds the long journey increasingly tedious and tiring until his young owner goes missing on the trail and he must use all his skills to find her.