Ken McLaughlin's (Roddy McDowall) mare Flicka gives birth to an all-white colt that, unknown to Ken's dad, Rob (Preston Foster), was actually sired by a neighboring rancher's thoroughbred racehorse, Appalachia, rather than Rob's own stallion, Banner. Ken's mother, Nell (Rita Johnson), names the colt Thunderhead after the billowing white clouds she sees overhead. Ken trains Thunderhead as a race horse, but the colt suffers an injury during his first race, ending his racing career.