Doctor Moulineaux, "serious and established" after a dissipated youth, lives a bourgeois life with his wife Yvonne and his servant Étienne. But he has gone to the Opera ball to win the heart of the elegant Suzanne Aubin. He arranges to meet her in a mezzanine that belonged to a seamstress. Impromptu visits from his acquaintances force him to pretend to be a tailor.