The secret agent of the Russian Emperor Alexei Kaverin received an unpleasant task: to kill in a duel an annoying admirer of Grand Duchess Alexandra Mikhailovna. The girl went to Nice for treatment and allowed herself to make inappropriate acquaintances. Imagine Alexei’s surprise when in the princess’s maid of honor he recognized Polina Serova, a colleague in special service and an eternal rival! But this was not the only trouble: the duel did not end at all as Alexey had planned. However, when he and Polina finally found a way to get rid of the dubious suitor of the princess, their plans were disrupted by an old acquaintance - the famous French detective Vidocq. He is looking for the French crown jewels that disappeared during the revolution, and now Alexey and Polina are forced to help him, because Vidocq has letters compromising the princess!