Child actor Mark Lester proved that his sudden ascension to stardom in Oliver wasn't a fluke with Run Wild, Run Free. Lester plays a psychosomatically mute young Dartmoor boy, who avoids all human contact whenever possible. He is fascinated by nature, but cannot convey this love to his unimaginative parents (Sylvia Sims and Gordon Jackson). Through the kindness of a retired colonel (John Mills), likewise a nature aficionado, the boy is allowed to help train a white colt. When the colt becomes trapped in a quagmire, the boy is able to use his voice once more to summon help. Run Wild, Run Free was originally titled The White Colt which was the title of the David Rook novel on which it was based.