Timothy Dennis, a talented high school football player, dreams of following in his late father's footsteps by playing at Notre Dame. Tim's dreams are shattered, however, when his little sister Jane informs him that their mother, Winifred, has just married Englishman Roger Carlton and has sent for her children to join her in England. Seething with resentment toward his new stepfather, Tim sets sail for London with Jane. En route, he has a shipboard romance with teenage vamp Flossie Sampson. Upon arriving in England, Tim learns that his mother has arranged for him to attend boarding school at Eton. When Tim objects, his mother pleads with him to give the school a six-month trial period and promises that once he completes prep school, he can go to Notre Dame. Jane, meanwhile, is won over by Roger's menagerie of dogs and horses. At Eton, Tim sneers at the boys' uniform of top hat and tails, but is befriended by a small boy bearing the title the Earl of Weeld whom Tim promptly dubs "Inky." When Ronnie Kenvil, an imperious upperclassman, bullies Inky, Tim objects and a fight breaks out between the two boys. Peter Carlton, Roger's son and the head boy of the house, breaks up the brawl. A strong believer in the American principle of equality, Tim objects to the hierarchy governing the upper and lower boys. Exercising his sense of American ingenuity, Tim decides to establish a committee of lower boys to buy the items required by the upper boys at a discount, then sell them to the upper boys at a profit. When Justin, the headmaster, discovers the plan, he deems it a disgrace worthy of punishment. Although Tim accepts total responsibility, Kenvil decides to pit the lower boys against him by exempting Tim from a caning. Soon after, Tim goes home for the holidays and is surprised to find how well Jane has adjusted to her new life. When Tim invites Flossie to a big party at the Carlton house, Flossie flirts with Peter, thus incurring Tim's jealousy. After Peter refuses Flossie's request to ride Bonnie Warrior, the Carltons' prize horse, she tricks Tim into taking her to see the horse. Spooked by Flossie's white dress, Bonnie Warrior gallops into a wall, forcing Roger to shoot the fatally injured horse. Remorseful over the death of the animal, Tim decides to run away back to America, but is intercepted by Roger, who escorts him into the family chapel and shows him the grave of Bobby, his young son. Roger then forgives Tim and assures him that he is not trying to replace his father. Encouraged by Roger to return to Eton, Tim experiences a dramatic change of attitude and begins to apply himself to his studies and participate in school sports. After winning a Rugby match for the team, Tim is awarded a cap bearing the school colors. Thus emboldened, Tim determines to beat Kenvil in the steeple chase. On the night before the race, Kenvil steals Justin's car to keep a date with Flossie. Noticing a figure breaking into the car, Peter hurries outside and watches helplessly as the vehicle speeds away. After Peter returns inside, Tim spots the handkerchief that he dropped lying on the ground and, assuming that Peter stole the car, sneaks outside to conceal the evidence. When Justin finds Tim wandering the grounds, he assumes that he stole the car and when Tim refuses to defend himself, confines him to his room. After a night of drinking with Flossie at the Willow Club, Kenvil climbs into the car, drunk, and drives off the road. While out motoring the next day, Jane spots the overturned car and hurries to Eton to talk to her brother. When Jane urges Tim to tell the truth, he confers with Peter and discovers that Peter dropped his handkerchief while witnessing the car theft. Determined to expose the thief, the boys hurry to the Willow Club to question the bartender. After a brawl ensues between the uncooperative barkeep and the boys, the barkeep agrees to identify the culprit and they all rush back to Eton, arriving just at the start of the steeple chase. When the barkeep informs Justin that Tim is innocent, Tim rips off his clothes and joins the race. As the runners streak toward the finish line, the barkeep identifies Kenvil as the car thief and Tim wins the race. All ends happily when, at the end of the term, Peter is accepted at Notre Dame and Tim replaces him as head boy at Eton.