Tomas is a prominent brain surgeon living in communist Czechoslovakia, who finds himself embroiled in an affair with the free-spirited Sabina, an artist based in Prague. During a visit to a serene spa town for a specialized surgical procedure, Tomas encounters Tereza, a discontented waitress yearning for intellectual engagement. Tereza tracks him down in Prague, leading to her moving in with him and complicating the dynamics of their relationships.
In a bid to help Tereza build a career as a photographer, Tomas enlists Sabina's help. As Tereza begins to see the connections between Tomas and Sabina, she experiences a pang of jealousy mixed with fascination. Despite their complicated situation, Tereza and Sabina develop a heartfelt friendship. Eventually, Tomas and Tereza wed in a simple, joyous ceremony, yet tensions arise as Tereza struggles with Tomas's ongoing infidelities. This emotional turmoil deepens when the Soviet Army invades Czechoslovakia, prompting Tereza to photograph protests against the regime. She ingeniously manages to pass her films to foreigners for safekeeping in the West.
Faced with the oppressive climate back home, Tomas, Sabina, and Tereza flee Czechoslovakia, making their way to Switzerland, with Sabina venturing out first, followed by the hesitant Tomas and Tereza. In Geneva, Sabina begins a passionate affair with Franz, a married professor, but ultimately decides to end the relationship when she realizes he plans to leave his family for her, fearing his attachment might weigh her down emotionally.
Meanwhile, Tomas and Tereza adapt to life in Switzerland, but Tereza feels alienated by the unwelcoming Swiss culture. When she discovers Tomas has resumed his promiscuous behavior, she makes the tough choice to return home. Hurt by her departure, Tomas follows her back to Czechoslovakia, where his passport is seized upon arrival, trapping him there. Yet, their reunion fuels their love.
Efforts to resume his medical career are thwarted by a critical article he wrote prior to the invasion, which makes him a target of the government. Refusing to retract his claims, Tomas finds himself blacklisted and ends up working as a window washer, all while continuing his womanizing ways.
Amidst these turbulence, Tereza encounters an engineer who propositions her during her waitressing job. In a moment of weakness, she engages in a fleeting, emotionless affair. Overcome with guilt, she fears that he could be an informant for the StB secret police, jeopardizing both her and Tomas's safety. Just when she contemplates ending her life at a canal, serendipitously, Tomas appears and persuades her to return with him.
Longing for a simpler existence away from the oppressive city, Tereza nudges Tomas to retreat to the countryside. They find solace living with an old patient of Tomas's in a serene village, escaping the political drama of Prague. On the other hand, Sabina embraces a wild bohemian life in the U.S. In a twist of fate, Sabina’s sense of shock comes from an unexpected letter revealing that Tereza and Tomas have suffered a tragic car accident.
In a poignant conclusion, the film portrays Tomas and Tereza driving along a rain-soaked country road just moments before calamity strikes, as Tomas joyfully shares with Tereza how genuinely happy he feels in that moment.
