Petr, a Czech teenager, begins working as a trainee in theft prevention at a grocery store. He is criticized by his employer for being too conspicuous and then, when he suspects a man of stealing, he is too nervous to stop and confront the man so he just follows the man around and then returns home, where his father admonishes him because the shop manager had come looking for him. His father peppers him with questions about how he acted and why he did not do anything to stop the man. Petr likes Pavla, who is dating Mara. Petr and Pavla go for a swim together and then lie on the grass, where they are yelled at by Čenda and Zdeněk, two apprentice bricklayers. Later, at a party, Čenda sees them together and repeatedly argues with Petr. He becomes upset when the master mason notices them fighting and blames Petr for making him look bad in front of the boss, then asks to borrow money. Petr lends him the money and Čenda buys more drinks to work up the courage to tell a girl in blue that he likes her, but the girl in blue has already begun to dance with someone else. Petr dances with Pavla but is unfamiliar with the popular moves. The next day Petr delivers two painting prints to the shop but one of them falls and breaks the glass and frame. He takes the print with him on a date with Pavla, who agrees to try to meet him again the next day. The next day at work Petr sees the thief he chased before and notifies his boss, but his boss shakes the man's hand and takes him into the back room. Confused, Petr watches a woman steal several items by hiding them in her bag and then leaving the store but he does not stop her. Petr gets in trouble again over the incident and once again faces a barrage of questions from his father about his behavior and why he failed to act. His father suspects that it was a retaliatory act for something that had gone wrong at the shop but Petr refuses to explain his actions. His father laments the fact that he invested in a violin and an accordion that remained unused while Petr bought a guitar that is unable to earn him any money. As Petr's father is yelling at him, Čenda knocks on the door. Petr's parents insist that Čenda come inside and sit down. Čenda returns the money that Petr lent him and Petr's mother offers him a piece of cake. When they learn that Čenda is an apprentice bricklayer, Petr's father makes Čenda show Petr his hands so that his son can see what hardworking hands look like. Zdeněk reminds Čenda that they must leave. Čenda attempts to stay because he finds the family fight interesting but when he is asked by Petr's father what is so interesting he backs away in fear. Petr's father continues with the argument, attempting to explain his perspective on what is important.
