A sad story about a young girl who is forced to move from one foster home to another.

"Why is my son stupid?" laments the poor Roma coal miner. His son Dilino is a nice boy, but he still causes his parents a lot of worry. He hasn't picked up much sense, so he's not much use to the coal family, and he's got all kinds of crazy ideas on top of that. For example, he began to force his unfortunate father to go and ask for the hand of the princess herself for him!

It all begins at Prague Airport, where American agents have brought Major Maisner, who has been expelled from the United States, in handcuffs. He returns to his place of work, the Central Police Academy, despite having been demoted to lieutenant for his "performance" and his position as academy commander having been taken over by the newly promoted Captain Hrubec. Maisner meets his former students, who now teach at the school. They all welcome him enthusiastically and receive gifts from him. While psychologist Kudláková, who is attracted to commanding types, has lost interest in the demoted Maisner and is now passionately in love with Hrubec, Boženka Vinklářová, who has broken up with the gypsy Štefan and now teaches dactyloscopy at the school, focuses her attention on him. Maisner recounts how he jumped off a skyscraper in America to defend himself against Simona Ptáčková's advances.