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....