Two kind but foolish sisters live together in their villa in a small town in South Bohemia. Fany (Natasa Gollová) has never married and Andelka (Eva Svobodová) is a widow. In the morning, the two sisters go into town. They need to buy fuel oil, put money in the bank and give plums to the teller. In the meantime an smallish orange Skoda MB car parks at their house, with Hermínka (Iva Janzurová), the old ladies' niece, and her fiancé Michal (Jirí Hrzán) in it. Michal has forgotten to bring flowers and has to go into town to fetch them. At the bank, Fany wants to deposit money but the minute the teller opens the safe, a thief arrives. He knocks the teller and Fany unconscious and runs away with the money. When Fany comes to her senses again, she sees Michal and accuses him of being the thief.
In the thick woods at the edge of the Bohemian Forest, two border guards are keeping watch - rifleman Kucera (Rudolf Jelínek) and dog handler Stencl (Josef Hajducík), whose sluggishness and clumsiness have won him the nickname Simpleton. The official army dog, the bitch Líza, picks up the scent of an alien dog on the German side - Black Wolf. She bites through her leash and runs away. Soon afterwards, the border boundary was interrupted. The two soldiers are wounded in the gunfire that follows, but Stencl's shot also hits the target and the intruder - an attractive woman in a black jersey - is dead. The investigation reveals that this agent knew someone among the local residents. The locals are all called in to identify the body but nobody admits to knowing the woman.
