There is then a love scene for Marie and Tonio, followed by a duet for them, "A voti così ardente" (No longer can I doubt it).
Afterwards the grenadiers sing a "Rataplan" chorus.
[[Listen]]
Rataplan, rataplan, rataplan,
But, alas, the Sergeant has been informed that the Marquise de Birkenfeld desires safe conduct. Birkenfeld! That is the very name to which were addressed certain papers found on Marie when she was discovered as a baby on the battlefield. The Marquise examines the papers, declares that Marie is her niece and henceforth must live with her in the castle. Poor Tonio has become a grenadier in vain. The regiment cannot help him. It can only lament with him that their daughter is lost to them. She herself is none too happy. She sings a sad farewell, "Convien partir! o miei compagni d'arme" (Farewell, a long farewell, my dear companions).
Act II. In the castle of the Marquise. Marie is learning to dance the minuet and to sing classical airs. But in the midst of her singing she and Sulpice, whom the Marquise also has brought to the castle, break out into the "Song of the Regiment" and stirring "rataplans." Their liveliness, however, is only temporary, for poor Marie is to wed, at her aunt's command, a scion of the ducal house of Krakenthorp. The march of the grenadiers is heard. They come in, led by Tonio, who has been made a captain for valour. Sulpice can now see no reason why Marie should not marry him instead of the nobleman selected by her aunt. And, indeed, Marie and Tonio decide to elope. But the Marquise confesses to the Sergeant, in order to win his aid in influencing Marie, that the girl really is her daughter, born out of wedlock. Sulpice informs Marie, who now feels that she cannot go against her mother's wishes.
In the end, however, it is Marie herself who saves the situation. The guests have assembled for the signing of the wedding contract, when Marie, before them all, sings fondly of her childhood with the regiment, and of her life as a vivandière, "Quando il destino, in mezzo a strage ria" (When I was left, by all abandoned).
The society people are scandalized. But the Marquise is so touched that she leads Tonio to Marie and places the girl's hand in that of her lover. The opera ends with an ensemble, "Salute to France!"