The scene of the opera is laid near the Dragoman Pass, Bulgaria, 1885.  Servia and Bulgaria are at war.  The family of Col. Popoff, of the Bulgarian Army consisting of the daughter Nadina, Aurelia, the mother, and Mascha, Aurelia's cousin, are ensconced in their home, fearful of the approaching engagement between the conflicting armies.  Nadina, a romantic maiden, is in love with Alexius, a young Bulgarian who has become a hero amongst his countrymen for his brilliant Cavalry charge against the Servians.  This young officer is idealized by Nadina, and she is filled with complete admiration for this conquests.

Lieut. Bumerli, a young Swiss officer, attached to the commissary department of the Servian forces, is attacked by the patrol, whom he eludes by climbing into Nadina's boudoir.  His suave manners, compelling arguments and quick wit under difficulties force Nadina to conceal him, against her will, and he is saved by the three women who greatly admire his youthful mien and carriage.  Later Bumerli, who has engaged in this flirtation with Nadina to save his life, falls in love with her and she, almost against her will, yields her affections to the business-like, scientific Swiss soldier, who shows the half-savage Bulgarians what training and education accomplish against their bombast and mock heroics.

The sentiment of The Chocolate Soldier is evoked by the love affairs of Bumerli and Nadina, Massha and Alexius. The comedy is furnished by the episode of Col. Popoff's house coat which is loaned to Bumerli in order to make his escape, its return, and the fact that the photographs of the three women are hidden in the pockets.