Jane Gershon and her fiancé, Eric Woodhouse, separate in Germany upon the outbreak of war. Later, they meet in the British fortress at Gibraltar as German spies, Jane posing as the daughter of a friend of the governor’s family and Woodhouse as a British officer. Eric surprises Jane trying to obtain the key to the mine-control field in the harbor; she tries to dissuade him from destroying the British fleet; and noticing a gun covering her, he surrenders and feigns suicide. A trusted Hindu servant, Amahdi, denounces her for being a traitor to the Fatherland, threatens to kill her, and is shot by Eric before he can destroy the fleet. Jane discovers that her lover is a British agent, like herself, and they are united under one flag. More on Wikipedia or Mubi
Watch Inside The Lines (1930)