A short book about a Spanish boy and a horse is set on a ranch in the Southwest and solves a routine mystery in its narrative of training, ranching and performances. Gruyo, born of a Palomino mother but covered with the mottled grey markings that indicate the particular characteristics of his father's breed rather than the palomino, is given to Gavvy Martinez, who lives near the Turnbull ranch. During the next three years Gavvy's fun with the colt is marred by the animosity of Bud Barnsley, whose father has a feud on with Mr. Trunbull. But a mysterious shooting and the saving of Bud in a race reveals an outsider's attempts at theft and patches up the old score between the two men. In all this Gruyo and Gavvy are the principles.