"I Was a Spy" tells the true story of Belgian nurse Marthe Cnockaert (Madeline Carroll) who saved the lives of soldiers on both the German and allied side. Marthe was also a spy who risked her life for her country. In 1915 while Belgium is occupied by the Germans, Marthe Cnockhaert becomes a volunteer nurse at a military hospital in Roulers, treating both German and captured allied soldiers. She becomes a spy for the allies, which leads to a romance with Stephan, a German officer who is the secret leader of the liberation movement. After many daring adventures, Marthe is captured, but the gallant Stephan turns himself in so that she will not be executed. Marthe is imprisoned for the duration of the war, and when she is freed by the allies, she cries with joy as she realizes the good that has come from her and Stephan s sacrifices.