In 1962, brothers Bob and Horatio run a traveling circus, remaining on good terms despite carrying different ambitions. During a performance in Indiana, their gypsy partner Esmerelda introduces them to her daughter Talia. The two brothers are instantly infatuated by her, but Talia gradually ends up falling for Bob, slowly infuriating Horatio. When the two become engaged, Horatio tells Bob to choose between Talia or himself to spend his future with. Bob ultimately decides to stick with his heart and marries Talia. On their wedding day, Esmerelda gives the couple a mysterious box as a gift, which allows for them open a new circus; Buffalo Bob's Rootin' Tootin' Animal Circus, known for their magical animals performing defying stunts. Years later, Bob's young nephew Owen falls for a girl named Zoe during a performance at the circus. When they grow up, Owen proposes to Zoe with a clown's red nose in the middle of the circus ring. Everyone at the circus is initially excited until Zoe's father Mr. Woodley coerces Owen into proving himself as a capable provider by leaving the circus and going to work for him at his dog biscuit factory, where he is given the position of taste testing. Meanwhile, Horatio, whose success has been greatly depleted since his and Bob's split, begins sneaking into his brother's circus at night trying to find the secret to the magic animals; one night, he gets into a scuffle with the circus pets Old Blue and Zena, and accidentally starts a fire as a result. Owen learns later that Bob and Talia died in the fire, and he and Zoe, along with their daughter Mackenzie attend their memorial service at the burnt down circus. Horatio makes an unexpected visit at the service, announcing that he is going to take over the circus because of what he perceives to be Bob's betrayal for stealing Talia and severing their partnership years earlier. He and his henchmen then start a brawl, causing Owen, Zoe, and Mackenzie to flee the service. Before they leaving, however, Old Blue and Zena give them the mysterious box that allowed for the start of the circus. In the car, Owen discovers that the mysterious box holds animal crackers. During a stop, Owen inadvertently eats one of them and turns into a hamster. To figure why he turned into one, they return to the circus after finding a note explaining the cookies. They learn from clown Chesterfield that the animal crackers are the secret to the circus; they will turn the user into the animal they eat, and that it always remains full of an unlimited number of animals, but there is only one human cookie that can change them back to their normal selves. Later, he tells the couple they have inherited the circus. While Zoe is excited, Owen, still wanting to prove himself to Mr. Woodley, is resilient, and decides to remain at the dog biscuit factory. He continues his job there while Zoe restores the circus. Mr. Woodley, angered that her daughter left her job, begins to consider her fellow employee Brock, an egotistical saboteur, to become his successor. Zoe persuades Owen to come to the grand re-opening of Buffalo Bob's Rootin' Tootin' Animal Circus, however, it turns to be a disaster when the audience finds out that there are no animals at the circus. Owen is first reluctant to do something, acknowledging he is not a performer, but is otherwise persuaded by Mackenzie, the other performers, and the dying audience. While he is first uneasy about performing stunts as an animal, he soon grows to enjoy it, and by the end of day, Owen decides to quit the dog biscuit factory, declaring that circus is his family. However, as he finishes packing up at the factory, Brock unwittingly takes the animal cracker box, eats one of the cookies and turns into a mandrill. To catch up with Brock, Owen turns into a lion, but Brock falls out of a window, where Horatio's henchman Mario Zucchini takes the box before Owen comes out and frightens him, causing him to drive off with an unconscious Brock, and leave the box. Returning home, Owen realizes he lost the human cookie, meaning that he will be an animal forever. Zoe does not accept this, but has hopes that Owen can adjust to life as a certain animal. Woodley's employee Binkley, who has been trying to come up with a new type of dog biscuit, discovers the magical animal crackers, and she persuades Mr. Woodley to go to the circus to see his family. Weeks pass, and Owen is unable find a suitable animal to remain as, and the stress begins taking its toll on his relationships with Zoe and Mackenzie. One evening at the circus, Horatio arrives with Owen's human cookie (which he'd found in Brock's hand along with broken pieces of other cookies following Mario's return), offering to turn him back to normal as long as he turns over the circus to Horatio. Owen refuses, believing that he will remain an animal as long as he keeps his family together. Angered, Horatio forces Owen into the deal by bringing in his now-mutated animal henchmen, who were transformed by the broken pieces of the animal crackers Mario had taken earlier, and transforms him back by force-feeding him his human cookie. The circus performers discover Horatio's presence immediately afterwards, and work together to fight his henchmen, giving Owen back the box in the process. However, Horatio, dissatisfied with how they use the animal crackers, eats the remaining the broken pieces in his hand and turns himself into a chimera. Old Blue and Zena then reveal themselves to be Bob and Talia, explaining that they both survived the fire, but their human cookies were destroyed, forcing them to remain animals forever, and ask Horatio to stop his evil actions, and redeem himself. Horatio refuses, grabs them and tries to fly off with them. Owen, Zoe and Mackenzie work together to save Bob and Talia, and capture Horatio, with Owen turning him into a hamster as punishment. Mr. Woodley, who saw the performance, reevaluates his views on the circus, and allows Owen and Zoe to continue working there. He and Binkley decide to rework the failed dog biscuit experiments into a new circus souvenir. Owen and Zoe now work happily at the circus, with Owen going on the stage once more as a new transformation: a dragon.
