Set in the repressive landscape of 1953 Soviet Russia, follows Leo Demidov (Tom Hardy), an idealistic and decorated MGB (Ministry of State Security) officer who is a firm believer in the Stalinist system. His worldview is shattered when he is forced to witness the cover-up of a fellow officer’s son's death, which is officially ruled a "train accident" because the state doctrine insists that "there is no murder in paradise" —a belief that violent crime is a symptom of capitalism and cannot exist in a perfect communist society. The story unfolds through several key developments:

: While tracking the killer, Leo and Raisa are hunted by Leo’s psychopathic rival, Vasili (Joel Kinnaman), who is determined to stop them and protect the state's false image of perfection.

: The pursuit leads to a final confrontation in the woods with the killer, a former army doctor named Vladimir Malevich, and a brutal showdown with Vasili. Leo eventually manages to close the case by framing the killer as a Nazi agent to appease the state, allowing him to be reinstated and lead a new homicide division in Moscow.

: In exile, Leo discovers more dead children under similar gruesome circumstances. Realizing that a serial killer is operating along the railroad lines, he joins forces with a local general, Mikhail Nesterov (Gary Oldman), to conduct a secret investigation into the "impossible" crimes.