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.
Lom has just started working on the military airport, governed by Sudeten-Nazi Ullman. Resistance is quite active in the airport, collecting arms and grenades and communicating with allies. They have a lot of great intel thanks to secretary Jana Tomešová, who is Ullman's trustee and has access to a lot of restricted information. Jirka also starts working at the airport, but he is filled with sorrow and in need of revenge. He gets caught stealing a grenade and is arrested by the Gestapo, and later shot. When Jana sees him she faints and Ullman finds a secret message she had with her. He tells his Gestapo friends and goes to the warehouse to investigate where he gets killed by being pushed onto a transformer. The Gestapo start arresting and searching houses of airport workers, revealing that Marta is an informer for the Germans. Lom is not aware of this as he is still struck by Jirka's death. He picks the gun from his hideout and walks back to the airport. After the neighbours tell him the truth about Marta, Lom kills her and helps Jana escape.
Germans gather airport workers and threaten to kill them if no one says who killed Ullman. Then Lom appears saying he did it and kills some Gestapo officers, he is killed by the soldiers.
In the last scene of the film, a dying Lom has a vision of the future. He sees a woman with gun going forward with war atrocities around her. However she does not stop until the war is over and the Czechoslovak flag appears on a mast.
