Мinko, a storekeeper in "The Black River" logging camp courts his assistant Sevda. He goes down to the town hoping to be with her on New Year's Eve. There he spots his wife Donka arriving from the village. Minko keeps out of sight and Donka sets out for the "The Black River". The lorry driver Dobri joins her. During the long and difficult journey over the snow-covered mountain, the two are attracted to each other.

Abundant supplies of imported vaccine prove ineffective against an outbreak of foot-and-mouth disease epidemic in several population centers. Warehouse manager Rashkov has been found dead. Major Zahov has to investigate the case.

Professor Dimov is a diplomat who has been recruited as a spy by a foreign intelligence service. The suspicions fall on Dr. Belcheva. Major Kalinov is entrusted with the investigation of the case. He learns that she is Dimov's mistress. Paris, France. Dimov and Belcheva go out leaving a bag with secret documents in Belcheva's hotel room. Kalinov manages to retrieve the documents. After this incident Belcheva dies in hospital from poisoning. On board the plane Kalinov exposes the professor as a spy. Bulgarian counterintelligence officers arrest him.