Victor Ace loves to sing, but is forced to become a car mechanic. Lisa dreams of urban life, but lives in a village. Kostya Lastochkin is an excellent mechanic, but he serves in the army and comes home only on vacation.

Junior Lieutenant Maleshkin, an unshooted graduate of the school, commands the crew of the self-propelled gun SU-100. All the subordinates of Maleshkin are older than him and much more experienced. The authority of the young commander is tested at every step, he quarrels, then reconciles with his crew.