Mysterious Lady, The (1928)
Directed by Fred Niblo, with treatment and continuity provided by Bess Meredyth (A Woman of Affairs (1928)), this Greta Garbo silent's plot is remarkably similar to Mata Hari (1931) which features a woman spy who's pursued by her foreign handler while she falls in love with her prey. The print I saw on TCM was pretty scratched up.
Tania Fedorova (Garbo) is the titled woman who happens to be alone in the Vienna theater box for which Austrian Captain Karl von Raden (Conrad Nagel) gets a returned ticket. Naturally, he's captivated by her beauty and, seeing that she hasn't a ride in the rain, he escorts her home in his carriage. There they spend a romantic evening together, with Karl playing the piano of a particularly romantic moment from the play they both watched. After Karl leaves, Tania reads her telegram from Boris, that is General Alexandroff (Gustav von Seyffertitz), who had set everything up such that Tania could steal some important military plans from the Captain. But the next day, Tania and Karl spend a magical day together, after which both are seemingly in love with one another. However, after Karl has left her at her residence, Boris is there waiting.
At the train station, Captain von Raden is greeted by his uncle, and head of the Secret Service, Erich (Edward Connelly), from whom he learns Tania's identity and true profession. He is told to have nothing further to do with Tania even while he's entrusted with transporting the important plans. Tania surprises him on the train and they have a row about whether she really loves him or not. Though she claims that she indeed does love him, Karl demands that she leaves. However, shortly thereafter, General Alexandroff is shown congratulating Tania for getting the plans, which he then locks in his safe. And Captain von Raden is shown being disgraced and then jailed as a traitor.
Erich visits the Captain in the jail and arranges for his release such that he can enter Russia as a pianist in order to steal back the plans from Alexandroff. He is asked to provide the music for a private party which turns out to be in Tania's honor. Seeing her, he plays the piece from the play and she sings for the guests. Max Heinrich (Albert Pollet) is shown to be the real traitor. Later, Tania sneaks Karl a note requesting a clandestine meeting during which she demonstrates her love, after having opened the safe, by giving him the plans as well as the means to escape.
*** SPOILERS ***
Before Karl escapes, Tania tells him that the real traitor is Heinrich. After Karl escapes, she learns that the plans he's left with are blank. Karl is caught and Alexandroff accuses Tania of complicity. Left alone, she shoots the General and then, fooling the others into thinking Alexandroff is still alive, she arranges for Karl to be left alone with them. Tania and Karl then escape with the real plans together.