The Mysterious Lady (1928)

Military captain Conrad Nagel falls in love with Russian spy Greta Garbo and must secretly travel to Serbia in order to exonerate himself from a treason charge. It’s a very bare bones espionage film, but Garbo is quite alluring as a spy. She’s great at being both seductive and stoic so that it’s not obvious whether she’s also in love or just doing her duty.   

Side Note: Included on the DVD for this film was the remaining fragment of The Divine Woman, a lost Greta Garbo film. Aside from the sadness of seeing any film lost, the available scene shows a delightful interaction between Garbo and Lars Hanson, the soldier she is in love with who is supposed to ship out on that evening.