The Mysterious Lady

The Mysterious Lady 1928 is an MGM silent film starring Greta Garbo, Conrad Nagel, and Gustav von Seyffertitz, directed by Fred Niblo, and based on the novel War in the Dark by Ludwig Wolff.

Karl is called away to duty, however. Colonel Eric von Raden Edward Connelly, his uncle and the chief of the secret police, gives him secret plans to deliver to Berlin. He also warns his nephew that the woman is Tania Fedorova, a Russian spy. Tania comes to him aboard the train, professing to love him, but he tells her he knows who she is. Dejected, she leaves.The next morning, when Karl wakes up, he finds the plans have been stolen. As a result, he is sentenced to military degradation and imprisonment for treason. However, Colonel von Raden visits him in prison and arranges for his release. He sends his nephew to Warsaw, posing as a Serbian pianist, to seek out the identity of the real traitor and thus exonerate himself. ........

Source: Wikipedia