Funny adventures of identical and in a same time very different twin brothers Sasha and Lesha Zavitaykin during the summer vacations.

A group of Soviet soldiers stops in a forest near Prague during a break between battles. An elderly soldier named Sherstobitov, who was assigned to go to the unit's headquarters to get mail, meets a Czech girl named Eva. On the way to the unit's location, the soldier would throw away his bicycle, lie down under a tree and sing Czech songs he had recently heard, and the girl would come to listen to them every day. Before leaving for battle again, Sherstobitov gives Eva a piano as a parting gift, which he found in an abandoned house on a nearby farmstead.