Hortensius announces the arrival of the wedding party. It is led by the groom's mother, the Duchess of Krakenthorp. Marie refuses to leave her room. Sulpice tells her that the Marquise is her mother. The surprised girl says she cannot go against her mother's wishes. She agrees to marry a man that she does not love. She is about to sign the marriage contract when the soldiers of the 21st, led by Tonio, storm in to rescue their "daughter". The guests are horrified to learn that Marie was a canteen girl. They change their opinion when she tells them that she can never repay the debt she owes the soldiers. The Marquise is so moved by her daughter's goodness of heart that she gives her permission to marry Tonio. Everyone joins in a final ""Salut à la France"".