The film takes place in the occupied Republic of Czechoslovakia after the assassination of Schutzstaffel-Obergruppenführer and General der Polizei Reinhard Heydrich, head of the Reich Security Main Office, the combined security services of Nazi Germany, and acting Reichsprotektor of the Protectorate of Bohemia and Moravia.

Jirka is a boy whose family was murdered in the village of Lidice as repercussions for the assassination of Heydrich.

He stays with his uncle, engineer Petr Lom and Marta, a young girl living next door, who works at the post office to help take care of the boy.

The Gestapo start arresting and searching houses of airport workers, revealing that Marta is an informer for the Germans.

After the neighbours tell him the truth about Marta, Lom kills her and helps Jana escape.