As the fur trade era is ending, lifelong frontiersman Tom Fitzpatrick is forced to adapt. He breaks away from the mountains to join his friend and legendary mountain man Jedediah Smith, who is now trading goods along the Santa Fe Trail. After weeks on the trail, their wagon train runs dangerously low on water, and Smith disappears after setting out to find a new water source. Though a desperate search turns up no sign of Smith, Fitzpatrick stumbles upon an orphaned Arapaho boy whom he takes under his wing and names "Friday." When the caravan finally makes it to Santa Fe, Fitzpatrick learns that Smith has been killed by Comanche warriors, ending one of the most remarkable lives of the frontier age. Afterward, Fitzpatrick informally adopts Friday, sending him to receive a formal education in St. Louis, and eventually locates and reunites him with his Arapaho family. Years later, while Fitzpatrick is guiding settlers along the remote trails of the West, he again encounters his adopted son.