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.

A Czechoslovak battalion, led by Captain Hloušek, conquers a Slovak mountain village two days before Christmas Eve 1944. Christmas and classical music is heard from nearby German positions. The soldiers get permission from their commanders to celebrate Christmas. The only one against is the austere second lieutenant Jílek, about whose past there are various rumours and whom the soldiers distrust. Captain Hloušek decides to reconnoitre the enemy positions, which, despite a minor incident, goes off without a hitch. The holiday of peace and tranquility can begin both with ours and the enemy...