I Was a Spy (1933)

TO ANSWER THE LURE OF HER LIPS WAS FATAL!

During World War I, a young nurse in a hospital in German-occupied Belgium is secretly feeding military information to the British. Complicating matters is the guilt she feels when she has to treat the German casualties inflicted as a result of the information she's passed on, and the fact that the local German commandant is falling in love with her.