In 1950s Soviet Russia, former war hero Leo Demidov works as a high-ranking officer in the state security administration. His life is upended when his loyalty is tested after he refuses to denounce his wife, Raisa, as a traitor. Relocated to a remote outpost, Leo begins investigating a series of gruesome child murders that the state refuses to acknowledge. The totalitarian regime's official stance is that murders do not happen in their utopia, creating an insurmountable barrier for justice. Determined to uncover the truth, Leo's pursuit puts him in direct conflict with his own government.

As Leo delves deeper into the case, he teams up with General Nesterov, who initially distrusts him. Despite the oppressive environment and constant surveillance from political adversaries, the two men discover that the murders are connected, suggesting the presence of a serial killer preying on vulnerable children. Their investigation uncovers dark truths about the very foundations of the Soviet state, challenging their beliefs and forcing them to confront moral dilemmas and personal betrayals. Amidst the paranoia and brutal crackdowns on dissenters, Leo's quest for justice becomes a dangerous struggle for survival against a backdrop of widespread suspicion and impending danger.