Book 1 is about a young girl named Katie. She is an orphan and was taken in by a woman and her husband, the Stevenses. One day Mr. Stevens brings home a wild, honey-colored mustang. Katie gradually makes friends with the wild stallion. When a man comes to the farm bringing news of land in Oregon, Mr. Stevens in very interested but his wife hates the idea. He decides they will go, but he will send Katie to an orphanage and sell the Mustang. Learning of this plan, Katie and the Mustang run away with the hired man intent on reaching Oregon.
In book two, Katie and Hiram (the hired man) buy a pair of oxen and a wagon. Traveling on they meet up with a wagon train and decide to stay with them. As always, Katie and the Mustang are inseparable. They seem to have realized their dreams about Oregon when Annie, the girl Hiram loves, is injured in a storm. Hiram chooses to stay with her, and Katie makes the hard decision of travelling on with the wagon train.
Book 3 starts off as Katie and the family she has chosen to stay with press toward Oregon. Large rivers, dry deserts, and broken wagons are only some of the dangers they must face on the way. Then the wagon train meets up with some travelling actors. They have some horses incorporated in their act, and Katie is curious. The only woman in the group starts teaching Katie to do riding tricks. Later, when Katie is threatened by a rattlesnake, the Mustang saves her life by killing the rattlesnake with his hooves. Oregon is almost in sight!
The last book in the series tells how they finally reach Oregon. I don’t want to say too much because it will spoil the ending, but just let me tell you that you will be surprised.