Milan, 1855. The beautiful Virginia, Countess of Castiglione, helps a young revolutionary painter, Andrea Pieri, to escape the Austrians. Passion breaks out between the two. Pieri portrays the woman in a sketch that arrives in the hands of Napoleon III, who instructs the diplomat Nigra, actually head of the secret services of Savoy, to track her down. He asked the woman to lend herself to a special patriotic mission: to support the efforts of the sàbauda diplomacy, seducing the Emperor of France and convincing him to put the question of Italian independence on the agenda of the Paris peace conference.

Virginia falls in love with Napoleon III. Empress Eugenia, who had hints of their love story, is shown a jealousy that could compromise her plans.