It is 1848 when Joshua McCullough and his family leave their home in St. Joseph, Missouri, and set off for Oregon on a wagon train. Though many of the other families on the trail suffer devastating losses during their long journey, Joshua's is spared. However, Joshua must conquer his fear of water during one dramatic crossing, when he heroically dives into a rushing river to save his younger sister Becky. The battered wagon train finally reaches Oregon after traveling over two thousand miles.