Russia, late 19th century. As the impending war with Britain looms, a mysterious device, a mechanical flea, is discovered in the imperial palace. The investigation is entrusted to a young officer, Pyotr Ogarev, who aspires to earn the trust of Emperor Alexander III. In his quest for truth, he teams up with Levsha, a brilliant but forgotten craftsman from Tula. Together, they embark on a journey of intrigue and danger. As they unravel the conspiracy, they must challenge the system, unravel family secrets, and make difficult choices between duty and passion. The fate of the country and their own lives hangs in the balance.