As the result of an early traumatic experience, 10-year-old Philip Ransome is mute, a psychological affliction that is worsened by the overbearing love of his mother and the exasperated impatience of his father. Following the failure of an attempt to cure the boy at a local clinic, Philip's mother gives up in despair and allows him to wander freely about the moors that surround his home in Devonshire. During these days Philip makes two friends: a retired army colonel known as The Moorman and a white pony that runs wildly about the moors. Naming the colt after himself, Philip devotes all of his time to his new companion--until the pony suddenly disappears. Realizing that Philip responds more to animals than people, The Moorman persuades a neighbor's little girl, Diana, to lend the boy her pet kestrel. While training the falcon under the tutelage of The Moorman and Diana, Philip catches a glimpse of his pony and chases after it, completely ignoring the bird attached to his arm. As a result, Diana's pet is badly wounded. The kestrel recovers, but it is accidentally killed a short time later. As Philip lapses into listlessness, The Moorman recaptures the colt and patiently teaches Philip to ride. During this learning process The Moorman discovers that Philip is capable of speech. Then, while riding on the moors, Philip, Diana, and the colt get lost in a heavy mist and the colt becomes mired in a bog. A search party, including The Moorman and Philip's parents, find them but cannot rescue the colt. Looking at his apparently doomed pony, Philip speaks a few loving words of encouragement, and the colt struggles to safety.