The play takes place during the 1885 Serbo-Bulgarian War. Its heroine, Raina Petkoff, is a young Bulgarian woman engaged to Sergius Saranoff, one of the heroes of that war, whom she idolizes. On the night after the Battle of Slivnitza, a Swiss mercenary soldier in the Serbian army, Captain Bluntschli, climbs in through her bedroom balcony window and threatens to shoot Raina if she gives the alarm. When Russian and Bulgarian troops burst in to search the house for him, Raina hides him so that he won't be killed. He asks her to remember that "nine soldiers out of ten are born fools."