Desperate to spark some happiness in her lonely grandson, Champion, Grandma gives her boy a bicycle. Years later, Champion is training for the Tour de France with help of loyal Grandma and their overweight dog, Bruno. During the course of the big race, Champion and two other racers are kidnapped by a pair of box-shouldered thugs. The racers are taken to Belleville where they are forced to be part of an elaborate gambling event. Grandma however isn't about to let her boy go so easily and she and Bruno travel across the ocean--by paddleboat, no less--to search for Champion. Belleville is an immense city and it isn't long before Grandma and Bruno are hungry, lost and penniless. Things are looking pretty bleak when their cause is joined by the former scat singing jazz prodigies turned experimental musicians, the Triplets of Belleville.