Now a successful and wealthy architect, Mark Wallace (Albert Finney) and his wife Joanna (Jo) Wallace (Audrey Hepburn) fly their white Mercedes 230SL roadster to Northern France, in order to continue driving to Saint-Tropez to celebrate the completion of a building project for a client, Maurice. Tensions between the couple are evident, and as they journey south they both remember and discuss several past journeys along the same road.
The earliest memory involves how they first met on a ferry crossing when Mark was travelling alone and Joanna was part of a girl’s choir. They meet again when Joanna’s choirbus goes off the road and Mark helps get them back on the road. When the other girls get chickenpox, Joanna and Mark unexpectedly wind up hitchhiking south together.
The next story tells how the two newlyweds are travelling with Mark’s ex-girlfriend Cathy Manchester (Eleanor Bron), husband (William Daniels) and daughter Ruth ‘Ruthie’ (Gabrielle Middleton) from the USA. Ruthie is not given any limits, and her behaviour frustrates Mark and Jo. Eventually Ruthie reveals the unkind descriptions of Joanna her parents have made in private. At this point Mark and Joanna decide to travel alone.
Next the pair drive a new MG which begins to have exhaust troubles, finally catching on fire. On this journey Joanna announces that she is pregnant. They also meet the wealthy Maurice Dalbret (Claude Dauphin) and his wife Françoise (Nadia Gray). Maurice becomes a generous but demanding client for Mark.
The next story shows them travelling with their young daughter Caroline (Kathy Chelimsky).
Another time shows Mark travelling alone and having a fling with another motorist, but which is shown to be fleeting and unserious in nature. Later Joanna has an affair with Françoise’s brother David (Georges Descrières), which is portrayed as much more serious than Mark’s and threatens to end the marriage; however, while Joanna dines with David and they witness a couple eating together without saying a word, David asks, offhandedly, “What kind of people can eat an entire meal together and not talk?” Joanna replies, enthusiastically, “Married people!” and, realizing she misses Mark despite their faded passion, runs back to him.
At the end of the film, the Wallaces manage to end their long-term relationship to Maurice and find a new client in Rome. They honestly analyse their fears and insecurities which have plagued them throughout the film. Finally, they cross the border from France into Italy. This is new ground for them as well as for the audience, signalling a move beyond the old issues into a more mature future.