Hubert Hrabe, known as Smart Boy, is a Prague dandy who is always skirting the edge of the law. Like every likable rogue, he has a worthy adversary - Police Inspector Mourek, who has long been trying in vain to put him behind bars. However, this defender of justice, who is constantly trying to outsmart his "own" criminal, ends up becoming the victim of his own zeal while hunting forgers that are as good as any in Europe, as Hubert the Smart Boy, sets a trap for Mourek

It is 5 May 1945 and the uprising against the hated German occupiers has broken out in Prague. The Czech guards open the gate of the Pankrác prison to allow the prisoners to escape en masse. Many of them are shot dead by the German guards but young Ruda (Jaromír Hanzlík) manages to run away. He is taken care of by one of the Prague fighters, concierge Kytka. Kytka hides him in the flat of the house's owner where only the young maid Karla (Jana Brejchová) is left, ordering her to take care of Ruda.