It's 1931. Future Red Marshals and unfinished horse breeders of Tsarist Russia are engaged in improving the Oryol breed of trotters. The state is also engaged in selection on a large scale - the Soviet breed of people is being improved through violence and hunger, show trials and catching saboteurs. Investigator Zaitsev takes on the case of the death of horses. But it is no longer so important how he finds the criminal, the most important thing is who during the investigation he will be able to push out from under the hooves of the terrible red horse...