The action of the Russian detective mini-series "Trap for a Monster" takes place in the Smolensk region. Moscow investigator Sergey Kovalyov is investigating a crime - Colonel Yevseev and members of his family have been killed. Kovalyov hides from his superiors the fact that he was related to the victim. In addition, he manages to find out that a series of monstrous crimes were committed in different regions several years ago. The handwriting of the murders matches. Kovalyov succeeds in having the cases combined into a joint investigation.