A sincere provincial young man, Frantisek Koudelka leaves to work in Prague. For the trip he buys a computer made horoscope with biorhythms charts, marked according to his date of birth, there are trappy, precarious, unsuccessful and even critical days and few successful days. The clumsy luckless person Frantisek has finally a guidance for his life.

In the morning twilight of Prague, the dead body of the safe-breaker Toufar is found floating on the river Vltava with a knife in his back. Police inspectors visit Toufar's lover, the prostitute Anna Kulatá (Jirina Bohdalová), nicknamed Umbrella, and it is apparent that the moment before she opened the door of her flat, someone fled through the window. Umbrella is summoned for examination to the head of the criminal police - Police Councilman Vacátko Jaroslav Marvan, but although shocked by the photograph of the dead man, she does not confess to anything. Before Toufar, Umbrella lived with the safe-breaker Penicka (Radoslav Brzobohatý), who loved her very much and made her quit her street trade. But when he was sentenced to three years' imprisonment, Umbrella began to live with the brute Toufar, who chased her to street again. In the case of the murder, Penicka is therefore the prime suspect.