This is a typical story from the 'cold war' era. A group of kids play on a quiet street in Sofia. From a nearby window falls a key. The helpful youngsters quickly return it to the owner, but in the haste switch the keys. The unintentional error disentangles a whole spy story. The young detectives doubt the good intentions of the man they tried to help. It turns out that the key is from a secret apartment where saboteurs are hiding. The secret network is exposed to the authorities and the kids feel like heroes.
Follows the Bulgarian people's struggle for national independence in the period from 1875 to the Liberation from Otoman bondage.
Ani, a charming young girl, is a driver at Sofia Airport. She sends a letter to her boyfriend Boyan, a worker at a large construction site. The letter contains a single word "yes". Boyan starts preparing for a wedding. The Soviet pilot Andrey will soon return home after several years spent working with his Bulgarian colleagues. They arrange a farewell tour of Bulgaria for him on which Ani has to drive him. Because of mistaken jealousy, Boyan tears up his sweetheart's letter.
