Act I - In 1885 the Serbo-Bulgarian war is in full swing. Colonel Popoff of the Bulgarian army has gone to war, leaving his wife (Aurelia), daughter (Nadine) and niece (Mascha) at home. They miss their men who are fighting, especially Nadine, who sings of her absent fiancé, Major Alexius Spiridoff, when in through the window climbs a young officer in a Serbian uniform. He is Lieutenant Bumerli, a Swiss officer attached to the Serbian forces. He was attacked by a Bulgarian patrol, but has not been found. With his charm, quick wits and good looks, he persuades Nadine, half against her will, to conceal him. She mocks him for greedily devouring, chocolate drops, and nicknames him “The Chocolate Soldier." During their conversation Bumerli tells her the truth about her fiancé’s, Alexius’, courage, by telling her that his valor in battle was a sham. She’s very upset to hear what Bumerli is telling her and orders him to leave; but she is already beginning to fall for the smiling Lieutenant.

The military have arrived and wants to check their house for Bumerli. Nadine hides him and pretends to be asleep when they arrive, so the search is fruitless and they leave. His snoring betrays him and Bumerli is introduced to Nadina’s mother and cousin. Since they are longing for the sight of a man, they are enchanted by his good looks and charms. He explains that he cannot leave in a Serbian uniform, so the three women dress him in one of Colonel Popoff’s uniforms, and unobserved, slip signed photograph of themselves in the pocket.

Act II - Six months later the soldiers return home, and Nadine is not as enchanted with Alexius as she was before he left for battle. She finds him pompous and conceited, especially when he tells of his victories, which she knows have never happened. Colonel Popoff tells them about a funny Swiss soldier, Bumerli, who escaped into a bedroom window - only to have three women fall in love with him! Aurelia is wondering what to tell her husband about his missing coat, when in walks Bumerli, and is welcomed by the Colonel and asked to stay for the wedding of his daughter. The coat is returned before the photographs are discovered. The photographs are retrieved but by the wrong owners. Bumerli is in love with Nadine, and she is sad to see him leave, and presents him with a photograph only to find the one she removed for the coat was from her cousin, Mascha. Thinking she has been wronged she rushes away.

The guests arrive for Nadina’s wedding to Alexius. One of the guests is Massakroff, who was the solider who was searching for Bumerli six months previously, only to find him attending the wedding. Bumerli is captured and tells his story of hiding in Nadina’s bedroom. To make matters worse, Mascha, who is in love with Alexius, show him the photograph inscribed “Nadine to her Chocolate Solider”. He is shocked and calls off the wedding immanently.

Act III - Later that afternoon is spent sorting out the tangled love affairs of Nadine, Bumerli, Mascha and Alexius. Nadine writes a tart letter of farewell to Bumerli, but he is not easily put off, and is undismayed by the prospect of a duel with the hero Alexius. She finally gives in to the advances of Bumerli, only to find that he is a wealthy man with a castle in Spain, a place in Italy, a ducal estate in Germany and several Swiss chalets. Mascha surrender to the jilted bridegroom, Alexius, and the curtain falls on the happiest of endings.