Jesse (Ethan Hawke) and Celine (Julie Delpy) have changed since we saw them last in 1995’s Before Sunrise, and the snippets of flashback with which director Richard Linklater peppers the early moments tell only part of the story. The two characters who shared one magical evening in Vienna as free-spirited 20-somethings don’t look quite the same, it’s true. Faint lines crinkle at the corners of their eyes; both appear slimmer in the face, as though time had worn away the baby fat of their youth instead of thickening them around the middle.

Something else has eroded, too, since that 14-hour rendezvous—something that fuels a heartbreaking miracle of a sequel. Before Sunrise remains one of the most lyrical, deeply romantic films of the 1990s, but Linklater, Hawke and Delpy have built upon that foundation in a completely unexpected way. Time has taken Jesse and Celine’s moment together and deepened its significance—and darkened it, as well.

There’s no hint of that darkness when they first cross paths again. Jesse is on a book tour for his first novel, the tale of a young man’s brief encounter with a beautiful French girl; Celine comes to see him when his itinerary brings him to Paris. The how-have-you-been small talk begins in earnest—she has become a social activist; he has a wife and child—only gradually approaching the subject of why they never again met. A death in the family had kept Celine from the mutually agreed-upon reconnection later that same year; Jesse had been left waiting at the train station without any knowledge of why. And as the stories of the intervening decade unfold, it becomes clear how profoundly that one night affected them both.

The simple act of revealing whether Jesse and Celine ever reunited might strike the passionate fans of Before Sunrise as something of a minor heresy. Leaving the earlier film on a note of open-ended wonder, Linklater forced us to ponder whether it would be better for the pair to pursue a relationship complicated by distance, or to dwell forever in the afterglow of their perfect night.

Before Sunset risks answering that question, and it’s not a pretty picture. Jesse is in a loveless marriage he’s afraid to leave for fear of missing out on his young son’s childhood; Celine is working on the latest in a series of brief, disappointing affairs. The blissful interlude of Before Sunrise is re-cast as a shadow over their lives. They’re left in a stunted netherworld, waiting for connections that never measure up, wondering if the relationship that almost was is the one that should have been.

It would be easy for Jesse and Celine’s pain to play out as emotional immaturity—the never-quashed expectation that the first blush of infatuation can continue indefinitely—but the lead performances create fully realized, wonderfully human characters with incredible chemistry. The radiant Delpy again makes Celine a pitch-perfect mixture of intensely felt conviction and deep insecurity, while Hawke allows Jesse’s swagger to dissolve into uncertainty. Their conversation is a duet of attraction and repulsion—both wondering at recapturing that long-ago magic, both afraid that they’ll discover how much time they’ve wasted.

It all builds to two scenes almost unbearable in their awkwardness. One involves Jesse and Celine slowly, wordlessly ascending a staircase; the other finds Celine playing a mournful waltz for Jesse on her guitar, the plaintive lyrics like something out of a high school girl’s journal. Linklater guides his two leads to reactions of gorgeous, unforgettable simplicity. It’s hard to imagine another film this year providing quite as powerful an emotional one-two punch.

Before Sunrise closed on a near-perfect grace note, showing brief glimpses of the places Jesse and Celine visited during their Vienna night, places that would forever become part of an indelible memory. Before Sunset echoes that finale in its opening sequence, showing locations we know will eventually hold a similar resonance. The wonder of Before Sunset is that it imagines both the beauty and the pain of memories for those who have never been able to file them anywhere that makes sense. The road not taken has rarely led to such a beautiful, sorrowful place.