1865: Swiss captain Bluntschli fights as mercenary in the war between Bulgaria and Serbia. When his group's attacked by a few Bulgarian troopers, he learns that he's got the wrong ammunition for his cannon and has to flee. His flight leads him right into the bedroom of his enemy's fiancée.

Countess Franziska "is kidnapped" by a band of robbers. However, her father is not willing to pay the ransom so Franziska changes sides.