The story is set during World War I in Gibraltar. Jane Gershon (Betty Compson) and Eric Woodhouse (Ralph Forbes), who were engaged in Germany before the war separated them, are reunited at the British fortress. Both appear to be German spies with orders to destroy the British fleet anchored in the harbor. Unbeknownst to each other, both are actually British double agents. The German government, suspicious, sends a third agent, Amahdi (Mischa Auer), to ensure the sabotage is carried out. The film involves mistaken identities and dramatic twists as each protagonist tries to protect the other from being exposed as a spy, ultimately resulting in the reveal of their true allegiance and the defeat of the actual German agent.