A geologist engineer Yuliya disappears. Ablamov, an elderly engineer, organizes a rescue party to look after her in the mine galleries but they find nothing. Yuliya was last seen at a ceremony for award-wining miners. The newsreel crew was filming the event. Yuliya left in the middle of ceremony. Prodanov, a headstrong and quarrelsome engineer, had followed her. Suspicion falls on him. However, the film sequences shot at the ceremony reveal that Ablamov reacted suspiciously to Yuliya's exit. Detected as the murderer, Ablamov attempts to cross the border but is caught. Yuliya had discovered that the ore contained uranium. Ablamov had replaced the samples in order to prevent the development of the uranium ore deposit.

The action takes place in the last years of the Second World War, immediately before the socialist revolution in Bulgaria. It centers on the life of the middle-class family of Lazarov, which is torn by the sharp political contradictions taking place against the background of the popular struggle against fascism. The father Vitan goes through terrible mental traumas, which are the price, he has to pay for his illusions that in such clashes one can remain neutral and free from politics. The partisans execute the son Boris - a fascist officer, a sadist and a murderer. The daughter Lily is forced to search for her place in the conflict between the representatives of two hostile worlds - that of fascist brother and her husband - a communist and a revolutionary.