One night in a provincial French city, Marc (Benoit Poelvoorde) meets Sylvie (Charlotte Gainsbourg) after missing his train back to Paris. They wander the streets until morning, talking happily about everything except themselves, in rare, almost choreographed, harmony.
They arrange to meet again and Marc takes the first morning train back to Paris. When misfortune befalls Marc and prevents him from keeping the date, he searches for Sylvie... only to find someone else: Sophie (Chiara Mastroianni). What Marc doesn't realise is that Sophie is Sylvie’s sister. When Marc and Sylvie inevitably meet again, they find their unparalleled harmony still blossoms... but is it too late?