Elder brother Dima goes on tour with his school theater to the Krasnodar region. Younger brother Alyoshka goes to a military unit commanded by Uncle Borya, a brave tank colonel. Alyoshka becomes the “son of the regiment” in the unit. He carries out difficult military service with his characteristic resourcefulness and dexterity. Finds true friends and secret enemies. Quite by accident, he learns that two careless soldiers are preparing to steal military weapons from army warehouses for some criminal group. To prevent this crime, Alyoshka uses his entire arsenal: intelligence, cunning, ingenuity and... armor-piercing tank shells...