In 1910, the arrival of Col. Sam Castle’s Great American Circus captures the interest of young orphan Toby Tyler, who sneaks away from his uncle Daniel and aunt Olive's farm in order to watch the circus parade. Having only a penny, Toby must sample the show’s many delights from afar, but attracts the attention of shyster concessionaire Harry Tupper, who seduces him with tales of the excitement of working for the circus. When Toby returns home, Daniel excoriates him for failing to feed the hogs, which stampeded and ruined the crops. Although Olive tries to calm Daniel, he tells Toby that he is nothing but a burden to them. Crushed, Toby runs away that night and finds Harry, who welcomes him aboard as his assistant. As the circus group packs to leave, Toby’s dinner of one banana is stolen by chimpanzee Mr. Stubbs, and the commotion attracts the attention of Castle. The manager gruffly orders strongman Ben Cotter to take Toby with him atop his wagon, and although Ben glowers as if furious, he is secretly gentle and kind, and his songs help Toby sleep through the long night. In the morning, Toby follows Ben, prompting the other workers to tease the big man for his “small shadow.” After threatening the men into silence, Ben puts a stop to Harry’s habitual mistreatment of his helpers, throwing him in a pond after Harry shoves Toby. In the lunchwagon, young bareback performer Mlle. Jeanette invites Toby to sit with her, but her partner, arrogant young M. Ajax, commands that he leave. The boy is soon rescued by clown Sam Treat, who insists that Toby join his “family,” which consists of five performing dogs. Upon hearing that Toby has run away and feels he cannot return until he has earned some money, Sam gives him a pouch in which to save his wages. On his first day of work, Toby dutifully sells candy, but is distracted by the acts such as dancing elephants and trapeze artists. Afterward, Harry “generously” allows him to keep one-third of his tips, but works the boy unremittingly. When Toby sets down a candy tray near Mr. Stubbs’s cage, the animal eats the whole tray, soon falling ill. Toby brings him to Sam, who gives him castor oil and sends him to sleep with Toby, and a hesitant Ben allows the chimp atop the wagon as they travel that night. In the morning, a breakdown causes a delay, and to make up for lost time, they must parade directly through town before setting up their tents. The town is in the midst of a Fourth of July celebration, and the firecrackers frighten Mr. Stubbs, who jumps on the horses, causing them to rear, and the wagon to tumble over. The monkeys are loosed on the town, and although most are soon rounded up, Toby finds Mr. Stubbs in the sheriff’s office, waving the lawman’s pistol while the prisoners cower in fear. When a sharpshooter offers to kill the chimp, Toby runs into the office, approaching Mr. Stubbs gently until he can disarm him. Although Castle first fires Ben in a rage for allowing the chimp to topple the wagon, the publicity from Toby’s brave rescue doubles the circus’ profits, prompting Castle to demand that Toby and Mr. Stubbs travel on the wagon together from now on. Three weeks later, while Toby is watching Jeanette perform, her interest in him provokes Ajax’s jealousy. The performer proceeds to show off, resulting in a broken leg. Castle is horrified to have to cancel the show until Jeanette announces that Toby told her he was a horseback rider, and Castle suggests that Ben teach the boy to take over for Ajax. Harry protests strongly, forcing Castle to pay him an extra $20 per week “finder’s fee” for Toby’s services. On the wagon that night, Toby confesses to Ben that he lied about his horsemanship to impress Jeanette, and Ben intimates that Toby has saved enough money to return home. Mr. Stubbs, however, empties Toby’s pouch of coins while the boy sleeps, and in the morning Toby berates his friend. Ben gives Toby enough money to leave, but is pleased when the boy prefers to stay and face the challenges of performing. With only two weeks to train him, Ben is worried that Toby is hopeless, but by encouraging his competition with Ajax, Ben is able to drive Toby to succeed. Meanwhile, Harry has been confiscating letters to Toby from Aunt Olive describing their remorse and their need for Toby to return to help them with the failing farm. On the day of Toby’s premiere, the performers present him with a new costume, and Jeanette kisses Toby for luck. Toby ties up Mr. Stubbs, but the chimp breaks free and finds Olive’s most recent letter in Harry’s coat pocket. Toby has no time to read it before his performance, during which Ben and Castle hold their breath, but the boy is a huge hit. Afterward, he races backstage to read the letter and immediately packs to leave, not knowing that Mr. Stubbs is following him. When Harry discovers that the boy has disappeared, he trails him in a car, announcing in town that a boy has run away with a valuable chimp. Meanwhile, Mr. Stubbs finds Toby in the nearby woods and the two proceed along together, but when a hunter happens upon them, Mr. Stubbs runs up in the tree, where the hunter mistakes him for quail and shoots him. Harry arrives to find Toby sobbing over the prone body of his friend, and after informing the boy that the accident was his fault, Harry brings him back to the camp. Toby runs straight to Castle to explain what has happened, and is shocked and pleased to find his aunt and uncle there looking for him. They apologize to Toby and embrace him, while outside, Ben, who has learned about the hidden letters, dumps Harry into a barrel. That night, Toby is sad at the loss of Mr. Stubbs until Sam reveals that the hunter has brought the chimp back, grazed but unharmed by the bullet. Toby and Mr. Stubbs hug joyfully. Toby then performs one last show as Olive and Daniel beam with pride, during which Mr. Stubbs makes a surprise appearance by jumping on Toby’s back. The act is a huge success, and provokes Castle to declare “M. Stubbs” the new star of the show.