During World War I, Helene von Lorbeer, a nurse in a French hospital, poses as a German spy and is sent to England to gather important information about a secret British offensive. With the help of an Englishman working for the Germans, she is accepted as a guest in the household of Arthur Bennett, a prominent British war official. She discovers that Valdar, the butler, is also a German spy and that he will be giving her instructions. Helene attempts to uncover the identity of Schiller, the leader of the German spy system, but Valdar prevents her from doing so.
Valdar, suspecting that she is a British agent, attempts to kill her in the basement of the house. However, she manages to convince him otherwise and reveals that he is actually Schiller. He plans to use a time bomb to kill all members of an important cabinet meeting to be held in the house. But his plan is foiled and he is shot while trying to escape the British authorities.