This is the story of ""Caroloma"", which was one of the ""last of the open ranges to come under fence,"" the last of the truly wild mustangs -- and the Marriner children, Tenn, Michael, Ridi and Nancy, and their parents. When Mr. Marriner left for Denver, the family's cattle mysteriously disappeared, but without horses there was no way to retrieve the missing animals. Then the boys decided to try to trap horses. Their first attempts brought them only an old mare, whom the boys dubbed ""White Violet"" in disgust -- but she pleased the girls. Breathless chase brought Tenn the sorrel stallion he yearned for, and good fortune brought Michael Raven, a spirited black colt. For the insatiable horse market.