Fifth-grade students, misbehaving during an air-raid drill, smash a cabinet in the physics lab. Lev Prokushev, one of the perpetrators, takes a microscope eyepiece, which is soon discovered in Arkady Zubov's school bag. Arkady categorically denies any involvement in the mischief but refuses to name the culprit.
Arkadiy Zubov
Genya
Lyova Prokushev
Vitya Surikov
Lidochka
Katya
Classmate
Aronov, classmate
Seryozha
Marusya Ivanova, pioneer leader
Vladimir Vishnyakov, teacher
Arkadiy's father
Arkadiy's mother
School headmaster
Vitya Surikov's mother
Classmate
Doctor (uncredited)
Friend of Surikov's mother
