Based on the true story of four pioneering nuns in 1870 as they journeyed in a covered wagon from Santa Fe across the desert to Tucson to establish a mission hospital. En route, they are stranded when their horse is stolen, and are found by a cowboy, Carbine Webb, who is fleeing from an avenging posse. They ask his aid. Reluctantly, Carbine escorts them to the nearest trading post, and then rides on alone, relieved to have them off his conscience. But he's soon overtaken by the four women, who thank him profusely for his help. They are about to continue on alone when Carbine yells a warning. There's an Apache smoke signal ahead.