On the eve of the coronation of Russian Emperor Nicholas II, His Highness Georgy Alexandrovich arrives in Moscow with his children: Ksenia, Pavel and Mika . The day after the arrival of Ksenia Georgievna, little Mika, the governess Mademoiselle Declik and the faithful servant Afanasy Zyukin go for a walk. During the promenade, something terrible happens - Xenia is trying to kidnap the bandits . Fortunately, Erastus Fandorin comes to the rescue . But soon it turns out that the attempt to kidnap her Highness was only a distraction. They stole four-year-old Mika . For the life of a boy, a certain Dr. Lind demands the Eagle diamond, which adorns the imperial sceptre. Without this jewel, the coronation is impossible... And Fandorin comes up with a plan: to rent the diamond from Dr. Lind for the seven days that remained before the ceremony. During this time, the brilliant detective hopes to find a daring criminal and save the child. But will Fandorin succeed? After all, Dr. Lind is one of the most dangerous and cunning criminals, who is used to playing by his own rules...