In the charming coastal village of Sewels in Sussex, 12-year-old Velvet Brown and her older sisters, Edwina and Malvolia, joyfully celebrate the end of their school term, eagerly anticipating summer vacation. On her way home, Velvet encounters Mi Taylor, a young drifter, and engages him in conversation. During this encounter, she spots a magnificent and energetic gelding, known as The Pie, frantically chased by its owner, farmer Ede. Captivated by the horse's spirit, Velvet is even more impressed when Mi shares his knowledge about horses, leading her to insist that he join her family for dinner.
That evening, Mrs. Brown, who is unfamiliar with Mi, questions him about an address book containing her name, which he claims belonged to his late father. Although she chooses to keep her past with Mi's father a secret, she kindly invites Mi to stay the night in their stable. Velvet then attempts to persuade her father, Herbert Brown, a sensible butcher, to employ Mi as a delivery boy. Following a thoughtful conversation with Mrs. Brown, he changes his mind, and Mi is hired.
Later, Velvet confides in her mother about her budding affection for The Pie and inquires about Mi’s father. Mrs. Brown, a former swimmer, reveals that Mi’s father was her devoted trainer who inspired her to become the first woman to swim across the English Channel. She admits to withholding information about Mi’s father because she felt the timing was not right. Unbeknownst to her, Mi has just stolen money from the kitchen, yet he discreetly returns it and accepts the job.
Velvet entices Mi into joining her on a delivery to farmer Ede. During their trip, Mi shares that he has a deep-seated fear of horses after having been thrown from one. While observing The Pie in a field, the horse leaps over Ede’s wall and races toward the village. This robust display of agility prompts Mi to exclaim that The Pie could jump "Beecher's Brook." Ede, noticing the horse's chaos, decides to hold a raffle for him. Though Velvet's father initially forbids her from entering, Mi surprises everyone by purchasing raffle tickets for the entire village. Despite Velvet’s confidence that her numbered ticket, 62, will win, she is initially devastated when another number is drawn. However, fate takes a turn when the winning ticket is not claimed, and Velvet is awarded The Pie.
Eager to learn more about "Beecher's Brook," Velvet questions Mi, who reluctantly informs her it refers to a challenging jump at the Grand National Steeplechase. Her days are blissfully spent racing across the countryside with The Pie, until her father insists the horse must be utilized for work. Unfortunately, this plan backfires when The Pie bolts with the delivery cart, leading to Mr. Brown blaming Mi for the mishap.
Determined to prove herself, Velvet confesses to Mi that she has applied for entry to the Grand National, despite it requiring a hefty 100-pound fee. After hesitating, Mi acknowledges The Pie's potential to win, prompting Mrs. Brown to lend her daughter the money she earned from her famous swim. Velvet and Mi then set out to find a trainer and jockey, but their search proves futile. In a moment of vulnerability, Mi reveals his trauma from a past race that led to tragedy, preventing him from considering racing again.
In a twist of fate, Velvet decides to disguise herself as a male jockey for the race, enlisting Mi’s help to prepare. Though hesitant, she manages to fool the officials and participates in the arduous race, with The Pie starting at long odds. As horses drop out one by one, Velvet defiantly pushes forward, ultimately crossing the finish line and securing unexpected victory. However, her achievement comes at the cost of her disguise being revealed, resulting in The Pie's disqualification, much to Velvet's dismay. Despite this, Velvet becomes a national sensation, earning the nickname “National Velvet” as she captures the hearts of the crowd.
Back in Sewels, Velvet is inundated with tempting opportunities, including an offer from a Hollywood studio. However, she quickly declines, fearing for The Pie’s fate as a potential spectacle. Velvet’s father is initially upset but is reminded by Mrs. Brown that she understands the fleeting nature of fame. As Mi prepares to leave the Brown home, Herbert admits his previous distrust but acknowledges his newfound respect for the young man. Although Mi departs without a formal farewell, a grateful Velvet chases after him, finally ready to share the truth about his father.
