Mary Ellen is an orphan traveling west to join family, but members of the train reject her due to her surly disposition. Her only friend is Sally Mayhew, another girl traveling west with her family dying of consumption.
Mary Ellen Thomas is traveling west with Jenkins and his son to live with her remaining family. Her dad, Jenkins business partner, has passed away leaving her an orphan. Because of her rough life and treatment by the Jenkins, Mary Ellen has developed a gruff attitude especially toward adults. She is frequently in trouble and causes the Major and his men grief. She has one friend on the train Sally Mayhew who is dying from consumption. Her parents are taking her to Colorado for her health but have come too late to help her. Sally is confined to her wagon and is given a mouse by Mary Ellen for companionship. As a prank she puts it in a woman's sewing bag but Mary Ellen is blamed for it. As they approach the Rockies, it becomes apparent it will be too late for Sally so the Major decides to stop the train and have an early Christmas party for Sally. Mary Ellen knowing Sally, from Louisana, wants to see snow decides to go off on her own for it without telling anyone. On the way she finds ...Written by