Sergeant of the border troops of the KGB of the USSR Aleksandr Belov (Sasha Belyy), who is serving on the border with Afghanistan, is transferred to the reserve and returns home to Moscow. He is greeted by three faithful childhood friends - the eccentric major and the son of a professor of astrophysics Kosmos Kholmogorov (Kos), the cunning and enterprising Viktor Pchyolkin (Pchela) and the calm athlete Valeriy Filatov (Fil).