In this section, we rejoin Tereza and Tomas after their move back to Prague. Their life together continues with its familiar mix of personal and political turmoil. Tomas listens to a radio program sponsored by the police, who play tapes from dissidents' bugged apartments. Tereza rises every morning to have breakfast with Tomas, despite his protests; he would rather eat alone, but since their daytime schedules conflict, Tereza refuses to give up this chance to spend time with him.
Tereza's fear of the body persists. As she walks to the sauna one day, she watches the young women of Prague pushing their way through the crowd, and recalls the same young women in miniskirts taunting Russian soldiers during the early days of the invasion. In the sauna, Tereza watches one woman whose body she considers grotesque; the woman has a pretty, childish face but exaggerated curves. Before dressing, Tereza stares at her body in the mirror. She is embarrassed by her breasts and again puzzles over the supposed connection between soul and body. She wishes she could feel light about her body, and behave the way Tomas does.
No longer allowed to take photographs, Tereza works behind a hotel bar. A former ambassador works at the reception desk; she listens to him talk to a man whose son was identified by the police as a dissident. Tereza suddenly understands that the Russian police have been using the photographs she and other photojournalists took during the invasion.
In an effort at releasing herself from her fears of the body, Tereza begins flirting with men at the bar. Even this she cannot do lightly; she flirts heavily, seeming to promise too much too earnestly. A young boy gives her a hard time at the bar, and when he leaves, an older customer wrongly accuses her of having served a minor alcohol. A tall engineer intercedes on Tereza's behalf. He comes in days later, and the two flirt and he tells her he lives close by.
In a dream sequence, Tereza asks Tomas to help her. He directs her to Petrin Hill, where a man with a rifle helps three suicidal people kill themselves, then turns to her. She tells him no, and that it wasn't her choice, and leaves the hill understanding that Tomas sent her to die.
The dream makes Tereza decide to go visit the engineer. She goes to his room and the two interact awkwardly; they often lapse into uncomfortable silence. Sophocles' Oedipus is among the shelved books and Tereza thinks of it as a sign from Tomas. The stranger undresses her and the two have sex; at the point of orgasm Tereza spits in his face. She uses the toilet and feels she has been reduced to a body in the worst sense; the engineer's high-pitched voice breaks the spell, and she leaves.
On her way home Tereza notices a crow. Earlier she saw some children trying to bury it alive. She takes the bird home to save it, but cannot; she watches it die.
Later, Tereza returns to the sauna. She thinks of her affair, and realizes that it was the first time she had watched and seen during intercourse. This realization makes her want to see the engineer again; she imagines herself in love with him. He never arrives at the bar, however. The bald customer that gave her a hard time earlier calls her a prostitute and hints that people are watching her. The ambassador confirms that he is in the secret police, and after their conversation Tereza grows convinced that the engineer was in the secret police too, and that she was set up for blackmail.
Tereza and Tomas drive through Prague. The city has changed, and grown ugly. Russian words replace the original and traditional names. In another dream sequence, Tereza watches park benches float by in the river, and realizes the city is bidding her farew ell. She wants to die.
In Park 4, Kundera does not draw a sharp distinction between Tereza's reality and her dreams, which seems to imply that she is close to, or in the process of, losing her mind. Interestingly, Tomas appears only rarely in Part 4; Kundera uses his name mainly in association with the various miseries Tereza experiences. The couple does not communicate in this section.
The woman at the sauna with a pretty face and monstrous body stands, in Teresa's mind, for every human being, since she generally finds bodies disgusting. Her encounter with the tall engineer fits with this general disgust; she spits in his face and empties her bowels immediately after intercourse, associating sex with base bodily functions. The crow the children tried to bury seems to stand for Tereza's feelings about the body, since she feels literally buried by her own body.
Kundera continues to emphasize Tereza's inability to deal with lightness of being. Tereza cannot put a light interpretation on her one-night stand with the engineer; first she imagines herself in love with him, then she decides the engineer was a spy, and thinks of sex as an act of terror inflicted on her. Ultimately, it makes her want to die.
Just as Kundera makes us doubt Tereza's sanity by blurring the line between dreams and reality, he makes us question her again in light of the affair; we wonder whether truth or hysterical paranoia prompts her conviction that the engineer is a spy. The fact that we cannot identify the truth with certainty partly forces the reader to experience events as Tereza experiences them, and partly works to show the atmosphere of a police state. In a police state such as the one in which Tomas and Tereza currently live, any nightmare becomes a plausible reality.