The music of the opera is light and sparkling, the principal interest centring in the charming nature of the story and its humorous situations, which afford capital opportunities for comedy acting.  The scene is laid in the Tyrol during its occupation by the French.  Marie, the heroine, and the vivandiere of the Twenty-first regiment of Napoleon’s army, was adopted as the Daughter of the Regiment, because she was found on the field, after a battle, by Sergeant Sulpice.  On her person was affixed a letter written by her father to the Marchioness of Berkenfeld, which has been carefully preserved by the Sergeant.  At the beginning of the opera the little waif has grown into a sprightly young woman, full of mischief and spirit, as is shown by her opening song ("The Camp was my Birthplace"), in which she tells the story of her life, and by the duet with Sulpice, known the world over as “The Rataplan,” which is of a very animated, stirring, and martial character, to the accompaniment of rattling drums and sonorous brasses.  She is the special admiration of Tony, a Tyrolean peasant, who has saved her from falling over a precipice.  The soldiers of the regiment are profuse in their gratitude to her deliverer, and celebrate her rescue with ample potations, during which Marie sings the Song of the Regiment ("All Men confess it").  Poor Tony, however, who was found strolling in the camp, is placed under arrest as a spy, though he succeeds in obtaining an interview with Marie and declares his love for her.  The declaration is followed by a charming duet ("No longer can I doubt it").  Tony manages to clear up his record, and the soldiers decide that he may have Marie’s hand if he will consent to join them.  He blithely accepts the condition and dons the French cockade.  Everything seems auspicious, when suddenly the Marchioness of Berkenfeld appears and dashes Tony’s hopes to the ground.  The Sergeant, as in honor bound, delivers the letter he has been preserving.  After reading it she claims Marie as her niece, and demands that the regiment shall give up its daughter, while Tony is incontinently dismissed as an unsuitable person to be connected in any capacity with her noble family.  Marie sings a touching adieu to her comrades ("Farewell, a long Farewell"), and the act closes with smothered imprecations on the Marchioness by the soldiers, and protestations of undying love by Tony.

The second act opens in the castle of Berkenfeld, where Marie is duly installed, though she does not take very kindly to her change of surroundings.  The old Sergeant is with her.  Grand company is expected, and the Marchioness desires Marie to rehearse a romance ("The Light of Early Days was breaking"), which she is to sing to them.