Marie is overjoyed and greets her friends enthusiastically. Before she can say anything, the marquise walks back into the hall and declares that Marie is engaged to the duke.
The marquise coldly dismisses Tonio, then pulls the sergeant aside to speak with him privately.
Tonio stealthily returns to Marie to tell her he loves her.
Marie says that if he wants to marry her, he must first obtain the approval from all of her fathers in the 21st regiment.
Both are frightened by the battle between the French and the Tyrols and wait with the local villagers.
The marquise confesses that Marie is actually her own daughter, but does not want to announce it out of fear of being disgraced. Marie has mixed emotions; grateful she has been reunited with her mother, but sick to her stomach that she would have to marry a man she doesn't love.
When the duke arrives with his wedding party, no one can get Marie to leave her room. Marie ultimately decides to honor her mother's wishes and agrees to marry the duke.
The Marquise confirms Sergeant Sulpice's suspicions, stating that Marie is the daughter of her sister and was entrusted to the Marquise. When Marie returns from the camp, she is shocked to find out the news.
The Marquise is aghast by Marie's less-than-ladylike manners, and is determined to make her into a proper woman.