Captain of the NKVD, Yermolay Remizov—a merciless fighter against the enemies of the Motherland. On his group’s account are dozens of solved cases: eliminating the remaining White Guard remnants, capturing foreign spies, and rounding up Trotskyist accomplices. From reliable sources, Remizov receives a signal about a sabotage attempt being prepared at the Proletarian Diesel plant. The plant is the flagship of its industry, and any incident there will become a serious political event. The saboteurs must be identified urgently. But how? Unexpectedly, among the staff, the captain notices a new engineer—very similar to someone he knew since the times of the Civil War…