A West German businessman Friedrich Schmidt is arriving to Czechoslovakia with private mission and mission for Intelligence service. He wants to settle the old event from the time of the Second World War when he as a student of the Czech grammar school in the town of Kostelec took part at the denunciation of his schoolmate Pavel Richter. Pavel was during the period of Nazi terror following the assassination of Acting Reich Protector of Bohemia and Moravia Heydrich executed. Schmidt has also to enter into relations with persons suitable for cooperation with the West Intelligence service. Schmidt - earlier, before the German occupation Smíd - meets the schoolmates and endeavors to avert suspicion that arose already at the time of the tragic event.
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.
