When her mother dies, Mary not only becomes the household slave of her overbearing father, Scottish American Andy MacTavish, but also becomes a mother to her little sister Ruth at their home on the Dakota plains. Years later, Jack Fraser, the son of a surgeon at the nearby fort and a steady visitor at the MacTavish home, secretly marries Ruth although he is deeply loved by Mary. Sometime later, a baby is born to Ruth, and Mary, doubting her sister's assertion that she is married to Fraser, takes the child to the fort to find out the truth from Fraser himself. Andy, believing the baby to be Mary's, orders her from the house. In the meantime, the Indians go on the warpath and Mary is surrounded. Buck Mathews, a half-breed who has lusted after Mary, sees her with the child, and pitying the helplessness of the girl, leaves the Indians to protect Mary. Fraser arrives just as Buck is fatally wounded, rescues Mary, who forgives Buck before he dies. Fraser now acknowledges that he is the husband of Ruth.