Two Balkan countries, Nordhoff and Zandria, are enemies. Stephan Stephani has come to Zandria with his daughter Mary to dig up war secrets. Mary falls in love with Zandrian soldier Paul Ekaid, but when the animosities between the warring nations heat up, Stephan and Mary head for the border. There Mary encounters Vesta. Vesta has murdered Count Wenzel and stolen some plans. She sees Mary at the depot and convinces her to exchange passports. Vesta goes into Nordhoff with a copy of the plans written in invisible ink, and Mary winds up being arrested. She is to be shot at sunrise, but Vesta returns and sacrifices herself by changing places with Mary. Peace is declared between the two countries, and Mary is reunited with Paul.