OK 12 startuje.

The parents of twins Petr and Pavel are leaving for Afghanistan to build a dam. They entrust their offspring to their uncle Podlipný in Gottwaldov. The boys soon make friends with their new classmates. They are a little envious of their uncle, the pilot, because almost the entire class is interested in airplanes and attends a model-making club. Here, under the guidance of instructor Dáša, they build a model of an OK 12 airplane, with which they want to participate in a competition. The children assume that both Prague boys are also good at model-making. Petr and Pavel are ashamed to admit that they know nothing about this activity. To save their reputation, they decide to secretly learn it themselves.