1857. At a fort in the southwest corner of Wyoming, Sara Rowell, with her teenage son, seeks a guide who can take them west to join her husband through the Utah Territory—an impassable Wasatch Range at this time of year, a region populated by warlike Native American tribes, criminals of all stripes, and unpredictable Mormons. There are few willing to take such a risk, and the woman sets out on the road in the caravan of settlers, unaware that a young Native American girl has slipped into her wagon, having killed her father, a rapist, and fled into the wilderness.