July 1946. In the sparsely populated village Planina close to the Czechoslovak border, Vrsecký, Morávek and Vejvoda, the first three members of the Flying Unit of the National Security Corps, are beginning their service. They have arrested a man suspected of theft and during the prisoner's transfer Morávek meets Martina, daughter of the forester Bayer. Other men join the frontier guard regiment. The young couple's budding relationship ends tragically when Martina and her mother are both killed one night.