Marion Harley, the only child of a railway agent, marries Neal Cameron, a young engineer in her father's employ, and is disowned. Neal is unable to obtain employment, and heroines a prospector. They are very poor. When their only child is three years old, Neal decides to move to a new region, and they set out in their wagon to cross the desert. While the mother and father are busy making camp, the child opens the spigot of the water cask, a loss not discovered until next morning. The wagon is abandoned and they go forward on the horses. The horses in time become exhausted, and Neal and Marion struggle forward on foot. Besides carrying the child Neal must half carry Marion. Marion realizes that there is no chance for all of them, but that without her to hamper him Neal might win through and save the child. She therefore steals away while Neal is in an exhausted sleep. When he wakes and finds the note she has left, he realizes that she is right, and, though heartbroken to think that he must abandon her, takes the child and staggers on. Marion, after going as far as her failing strength would permit, has fallen unconscious, and is so found by her father, who, with a fully equipped party is inspecting the course of a new proposed railway line. She is revived enough to tell her story, and the party follows her trail. Neal is found unconscious but living, and the child is unharmed.