What a wild imagination the student of the 7th 'B' grade, Antosha Mylchenko, has! He imagines himself to be a great detective and now... he writes a detective story about himself. He also collects evidence, trying to find out what is happening behind the closed doors of the gym, where physical education teacher Pyotr Bronislavovich does not allow anyone, forcing poor children to run around in the snow and rain. Bronislavovich is being starved at home, so he commits atrocities - this is what Antosha decides. But what did your beloved teacher do wrong? This is what the great detective is going to find out. However, the investigation of this case quickly falls into the hands of his classmate Arina Balovantseva, and the detective has no choice but to put on his mother’s boots, hat and...