[3] The series centers on Rodion Meglin (Konstantin Khabensky), a highest level investigator of the Russian police who is also a sanctioned vigilante, hunting down the criminally insane ("maniacs" in Russian) who slip through the cracks of an ill-suited justice system.

A young law school graduate, Esenia Steklova (Paulina Andreeva), is assigned to the department of the Investigative Committee where Meglin serves, becoming his trainee.

Esenia has personal motives for working with the famous investigator - her mother was killed under mysterious circumstances, while her father hides key details of what happened.

Throughout the series, Esenia encounters unexpected challenges working with Meglin.

The creators of the Russian TV series reject the similarities of their work with the American TV show Dexter, but do confirm some commonality with the True Detective series.