This film had the potential to be among the finest espionage adventures I’ve experienced, if not for a truly dreadful conclusion! Nevertheless, Greta Garbo delivers an exceptional performance as the Mata Hari-esque agent working for the Czar and attempting to acquire information from Austria-Hungary. Following a shared opera box with him, “Tania” employs her considerable skills to seduce and deceive “Karl von Raden” (Conrad Nagel), a well-meaning but somewhat naive man, while he’s traveling by train. In doing so, she obtains state secrets, leading to his professional ruin, loss of reputation, and an extended prison term. Fortunately for him, his uncle holds a position within the secret police and helps arrange for the disgraced officer's chance to uncover who in their War Office aided Tania’s scheme. He assumes the role of a pianist and crosses paths with her at a party hosted by her lover “Gen. Alexandroff” – the spymaster who enjoyed watching Karl fall from grace. The pair then discover, unsurprisingly, that they are falling for each other. It's undeniable that Nagel and Garbo share an appealing connection; in fact, she seems to have chemistry with everything—animate, inanimate, or plant life. Regrettably, this romantic element ultimately undermines what was previously a captivating and dangerous spy narrative. Her allure shifts from sinister and effective to almost pitiable, culminating in an ending that descends into pure melodrama. Despite this, it remains a strong showcase for both performers, boasting meticulous attention to detail, and Fred Niblo maintains a brisk tempo, preventing the story from becoming stagnant.

Source on TMDB