During the First World War, the Russian officer Captain Ivan Ignatoff falls in love with his nurse, Natasha Kovrin. But she is subject to an upcoming marriage of family convenience to Brioukow, a wealthy industrialist of peasant stock. Brioukow is unjustifiably jealous, since Natasha has not betrayed him. He forces Ignatoff into his debt as a means of humiliating him. When Ignatoff's new friend, Madame Sabline, offers to pay his debt, preventing his ruin, Ignatoff comes quickly to realize that Madame Sabline has an ulterior motive, one that could prove dangerous to more lives than just Ignatoff's.