In 1966, architect Mark Wallace and his wife Joanna embark on a flight from England to France, intending to drive to Saint-Tropez for a meeting with Mark's long-standing client, Maurice Dalbret. As they journey, they reminisce about their earlier trips along this same picturesque route.
Their first adventure dates back to 1954, as Mark and Joanna meet on a ferry departing from England. While Mark is on a photography excursion, Joanna is traveling with her choir for a festival in Menton. Upon arrival in Dieppe, Mark becomes anxious, believing he has misplaced his passport, only for Joanna to discover it nestled in his backpack. Continuing their journey towards Abbeville, they encounter an accident involving the choir’s van, and Mark stops to offer assistance. He joins the girls en route to Abbeville, but as everyone except Joanna contracts chickenpox, it becomes just the two of them who travel southward. Despite Mark’s attempts to push Joanna away, she expresses her love for him, and they share a night together. Their time spent along the Mediterranean involves staying in modest accommodations and enjoying sun-soaked days at the beach. By the end of this memorable week, Mark proposes to Joanna.
Their second trip occurs in 1957, marking two years of marriage. They are accompanied by an American family, which includes Mark's former Chicago girlfriend, Cathy Seligman, her husband Howard Maxwell-Manchester, and their young daughter Ruthie. When Ruthie mentions that Cathy referred to Joanna as a "suburban English nobody," it prompts Mark and Joanna to part ways with the Maxwell-Manchesters, continuing their journey on their own.
In 1959, they travel independently as a married couple in a dilapidated vehicle. Joanna shares the news of her pregnancy. After their car unexpectedly catches fire, they are forced to take refuge at the luxurious Domaine Saint-Just. The following morning, they push their charred vehicle aside and soon meet the affluent couple Maurice and Françoise Dalbret, who were also guests at the hotel. The two couples decide to travel south together, eventually staying at the Dalbret villa in Ramatuelle, where Maurice introduces Mark to his business partner, Nikos Palamos. By the end of their journey, Maurice hires Mark for future projects.
With the arrival of their daughter Caroline, Mark finds himself traveling alone to France, where he spends the night with a woman named Simone. During this time, he deceives Joanna in his letters, claiming that he misses her.
In 1963, the Wallaces revisit France with Caroline to review the project Mark has been working on for Maurice and Nikos. While at the Dalbret estate, Joanna forms a connection with Françoise's brother, David, igniting an affair. After a night spent together, Mark confronts Joanna about this betrayal, leading her to confess her love for David. Ultimately, David offers Joanna the chance to leave Mark, but she chooses to return to her husband instead.
In the present moment, Mark and Joanna grapple with discussing the prospect of a divorce. They stop overnight at a hotel, where Mark becomes deeply absorbed in work, neglecting Joanna's presence. Upon arriving at a stunning residence designed by Mark for the Comte and Comtesse de Florac, they attend a party where Mark receives a phone call from potential client Hal Van Benius, who informs him of a job in the United States that will demand his presence for two years. Mark and Joanna decide to sneak away from the festivities; while driving through the serene forest, they candidly express their enduring affection for one another despite past grievances and unfaithfulness, realizing they cannot bear to be apart.
Later, they journey to meet Van Benius in Rome. As they approach the France–Italy border, Mark panics, thinking he has lost his passport, but Joanna has it under control. She playfully leaves it for him on the steering wheel while he rummages through the trunk. Their conversation bristles with tension as they exchange barbs, calling each other "bitch" and "bastard," before they continue their drive into the beautiful Italian landscape.
