In Paris in 1893, the dance-hall in Montmartre owned by La Môme Pistache, Bal du Paradis, is being threatened with closing by a self-righteous judge, Aristide Forestier. He is offended by the scandalous but popular dance that the attractive dancers perform at the dance-hall, the "Can-Can." The judge sends the police to harass the owner and dancers, but the police like the dancers so much that they are reluctant to testify against them in court. The judge decides to gather evidence himself, and takes a trip to the club. Once there, he and the owner, La Môme, fall in love. He tries to keep his identity a secret but the girls recognize him. He sees the Can-Can and gets photographic evidence of its scandalousness. La Môme and the dancers are sent to jail.
One of the dancers, Claudine, a laundry girl by day, has been pursued by Hilaire, an art critic, who plans to host to hold an elaborate ball at the club. Claudine, who loves a sculptor, Boris, arranges to have dinner with Hilaire so that her sculptor will receive a favourable review. Now, with the proprietress and dancers locked up, the ball cannot go forward. The judge is struggling with the conflict between his moral scruples and his love for La Môme. Eventually, he concedes that "obscenity is in the eye of the beholder". He urges her to escape, but a journalist gets a photograph of him kissing her – a scandal for him!
Hilaire criticises Boris's sculptures, and the cowardly artist manages to challenge the critic to a duel before fainting. Eventually, Hilaire writes a gushing review of Boris's work. Judge Aristide loses his judgeship and is disbarred, but La Môme and the girls all go to court with him and all win their cases.