A young prison guard, Josef Vildomec (Jirí Hrzán), returns home from the night shift to his widowed mother (Vera Tichánková), who is very proud of him. Her deceased husband was a gendarme and the son recently found a similar job. Every night before bedtime, Josef walks with his dog to an abandoned place and there severely beats the animal. To the prisoners, however, he behaves kindly and even gives some cigarettes to prisoner Cervinka (Karel Mares), who is in close confinement without food. The old thief and recidivist makes the naive Vildomec believe in his innocence and Vildomec begins to advocate him to his own cost.
