Nine years have passed since Before Sunset. Jesse and Céline have become a couple and parents to twin girls. Jesse struggles to maintain his relationship with his teenage son, Hank, who lives in Chicago with his mother, Jesse’s ex-wife. Jesse is now a successful novelist, while Céline is at a career crossroads, considering a job with the French government. After Hank spends the summer with Jesse and Céline on the Greek Peloponnese peninsula, Jesse experiences a disconnect with Hank when he drops him off at the airport to fly home and reflects on his inability to be a good father to him.
The couple discuss their concerns about Hank, and then about Céline’s career. Over dinner they talk more about love and life with friends. Two of the friends staying with them have prepaid for a hotel room for Jesse and Céline so that they can have a night alone. While walking to the hotel, the couple reminisce about their first meeting and wonder whether they would still be attracted to each other if they were strangers.
After reaching the hotel and checking in, they begin to get intimate and prepare to have sex but are interrupted by a brief phone call from Hank, who seems to have bonded with Céline more than he has with Jesse. The couple eventually have a fierce argument, expressing fears about their present and future together. Among other issues, Jesse wants them to consider moving to Chicago so he can be closer to Hank, which Céline thinks will cost her any chance of a career outside her family. In the heat of the argument, Céline tells Jesse she no longer loves him.
Céline leaves their room and sits alone in the hotel’s outdoor restaurant. Jesse joins her and jokes that he is a time traveler (referencing their first meeting) bringing her a letter from her 82-year-old self, describing this night as one of the best of their lives. Unamused, Céline says their fantasies will never match the imperfect reality. Jesse proclaims his love, saying he does not know what else she could want. After a moment, Céline joins in Jesse’s joke, and the two reconcile.