Stephen Stephani leaves Nordhoff with his daughter Mary to visit Zandria, an enemy country, where he tries to steal the war plans of the hostile nation. There, Mary meets Paul Ekald, a Zandrian captain, falling in love with him at first sight. While Mary remains in Zandria for the moment, Stephani returns to Nordhoff. Meanwhile, Vesta, Mary's illegitimate half-sister, has managed to get hold of important war plans stolen from Count Wenzel. But, to get them, she had to kill the count.