The comedy tells the story of a lonely mother of a small, naughty and immediate son who sometimes unwittingly does some mischief. Not for nothing does the mom say that in a family where they have such a boy, they would need a belt. The perceptive Petřík does not hesitate and goes to buy her a belt as a present at the department store. On this occasion, he invites the elderly nice saleswoman to their home, because their grandmother has already died and their father is gone too. In the shop, she meets a purse snatcher who tricks the boy for his address. On Christmas Eve, the mother is surprised not only by unexpected visitors at home, but also by a sympathetic young policeman who has accompanied her son home...