In 1811, Marie Dorion, a member of the Iowa people and mother of two boys, joins her husband on a harrowing overland expedition to establish a fur trading post in the Pacific Northwest. While her husband, Pierre, serves as the official translator of the undertaking, Marie soon proves to be his equal as they trade with Native Americans along the way. When their journey is bogged down by the poor decisions of the expedition's leader, who is more businessman than mountain man, the party nearly starves, and Marie is forced to bury her newborn third child in an unmarked grave. Though they eventually reach the safety of Fort Astoria, Marie's worst ordeal still lies ahead. While trapping in the mountains, her husband is killed in a Native American raid, and Marie struggles to survive the winter with her two sons in a hastily built shelter. When their meager supply of food is depleted, Marie sets out into a blizzard in a desperate attempt to find help, risking a lonely death to save her children's lives.