The action of the Russian detective mini-series "Mosgaz: Katran" takes place in the late 70s. Several bodies are discovered at a dacha near Moscow. The victims of this brutal crime are a young cardsharp named Kira Miller and a colonel of the Ministry of Internal Affairs from Volgograd named Viktor Potapenko. They were involved in a romantic relationship. Under the leadership of Major Cherkasov, a team begins the investigation. It turns out that shortly before her death, the girl lost 400,000 rubles at an illegal gambling establishment called "Katran."