Nine years after their second meeting in Paris, Jesse (Ethan Hawke) and Celine (Julie Delpy) are married to each other and the parents of two young twin daughters. They spend their summer vacation in Greece, together with Jesse's son Hank (Seamus Davey-Fitzpatrick) from his first marriage. When he flies back to America, Jesse is plagued by guilt over not being able to spend more time with Hank. Celine fears that Jesse will resent her for not being ready for a move to the U.S., thus keeping him away from his son.
But despite all the problems, the two still love each other, even though the dreamy, naive, and ill-fated love seems to be gone. Instead, they are stuck in a complicated, everyday relationship that becomes more of a challenge every day. Over the course of one vacation day, Jesse and Celine discuss the nature of romantic relationships with other couples, walk through Greece, and look back on their past.