With a sad heart, Blanche-Marie resigns herself to marry Aristide, whom she finds exceedingly uninteresting. On the other hand, and to the astonishment of her fiancé and the Marquis, Marie-Blanche goes to help at the shop at every opportunity. She realizes that she has made a mistake: her sister loves Gaston, and she herself would prefer the common life of the shop and marriage to Aristide. The day of the double wedding, Marie-Blanche looks for a portrait of the Marquis' wife. Her idea is to dress Blanche-Marie as the late Marchionesse. The resemblance is astonishing. The Marquis believes that he sees his wife: Blanche-Marie must be his daughter.