A screen adaptation of a novel by Janusz Korczak, the film offers insight into the mechanisms of governance using conventional production design and a small number of stage props. A child's naivety and idealism, as well as noble ambition to launch reforms and methods of their introduction result in huge commotion.
The story takes place in a fantasy realm where 10-year-old Maciuś inherits the throne from his father. However, real power remains in the hands of adults - the PM and his ministers, who treat the king like a spoiled kid. Maciuś wants to prove his courage. When a war breaks out, he goes to the front line posing for a regular soldier. He is accompanied by his friend Felek. The war is won. Maciuś learns about humility, perseverance and composure. He returns to the capital and decides to take over power. He befriends African king Bum-Drum, who gives him many gifts. Much to his surprise, Maciuś discovers the ruler's daughter Klu-Klu hiding in one of the chests; she becomes his friend. Inspired by a journalist, they form a children's parliament, which passes a law ordering adults to go to school, with their place to be taken by children. Great chaos ensues. One of the defeated kings decides to make use of this opportunity and the war breaks out anew. The child army is unable to defend the realm. The victorious evil king sentences Maciuś to death, then changes his mind and banishes him. Klu-Klu manages to save her friend by inciting the crowd, which starts to blow and consequently blows the enemy soldiers out of the city.
