
Sasha and Olya are getting married. Pchyola, Fil and Kosmos give young people an apartment as a gift. But on their wedding night, the young people almost die because of a stretching trap, to which a grenade is attached. Sasha notices the threat in time and almost manages to neutralize it, but because of the neighbor's dog, the grenade falls, and Sasha throws it down the stairs, where the explosion occurs.
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).
After defeating Mukha, Aleksandr Belov continues to live away from crime, and still plans to enter the Mining Institute. He also goes to buy a dog for himself, during the purchase of which he meets the famous stuntman and film actor Aleksandr Inshakov. Sasha does not suspect that he was on the list of Kaverin's personal enemies. Toiling from idleness, Sasha pays attention to the neighboring house, where the young violinist Olga Surikova is preparing for a performance. Sasha falls in love with her.