Our film begins with The Triplets of Belleville, a trio of singers, performing on stage in the early 1900s in Belleville (could be Paris), France with the likes of Josephine Baker and Django Reinhardt.
After the song ends, the story switches to Madame Souza. She’s an elderly woman raising her young grandson, Champion. Champion is a very sad and lonely boy due to the loss of his parents, so Souza does a variety of things to cheer him up. She tries to get him interested in playing the piano. That doesn’t work. She buys him a puppy named Bruno. That works for a short time, but soon he’s sad once again.
When Champion takes an interest in bicycle racing, she buys him a tricycle. (Champion’s parents may or may not have been cyclists themselves.) Years pass, and Champion is now a professional cyclist. Souza now acts as his coach.
Champion enters the Tour de France, but as it begins, two French mafia henchmen kidnap him and two other riders. They take the three to the bright, bustling metropolis of Belleville.
Souza and Bruno track the men, but they lose their scent soon once they reach the big city. Now lost themselves, Souza happens upon the elderly Belleville triplets. With their music hall days behind them, the women scrape by as improvisational musicians. The sisters take Souza to their home, and soon she becomes a part of their group.
Meanwhile, in another part of town, the main mafia boss drugs the kidnapped cyclists, and forces them to ride stationary bicycles for them to race; creating a little Tour de France of their own for the sole purpose of gambling.
We now see the Triplets and Souza perform a little jam session at a fancy French restaurant using a newspaper, refrigerator, vacuum cleaner, and bicycle wheel as instruments. The mafia boss who kidnapped her grandson is there too, and Bruno smells Champion’s scent on the guy. The doggie alerts Souza to him.
The next day, she finds one of the boss’ goons, and tails him. She finds Champion, and the boss’ betting racket. When night falls, several mob bosses and their henchmen arrive to place their bets on the riders. When one falls off his bicycle from exhaustion, the bookmaker shoots him as one would shoot an injured horse.
Madame Souza, Bruno and the Triplets then go into the hideout themselves, and sabotage the racing contraption thingy. Once it’s unbolted from the ground, it becomes a pedal-powered vehicle thingy. The mob chases after them, but in the end, their evil misdeeds are dashed. The reunited group happily rides away from Belleville.
We flash forward to the point Champion himself is now an elderly man, and all alone. He recollects this little adventure as his now dearly deceased Souza once told it to him.