PARK CITY - Prior to tonight's world premiere of Richard Linklater's "Before Midnight," I went back and revisited the first two installments of what has now become a trilogy. "Before Sunrise" and "Before Sunset" are incredibly easy watches at 90 and 80 minutes apiece. They have an easy flow, owing plenty to the writerly collaboration between the director and his stars, Ethan Hawke and Julie Delpy, which yielded a Best Adapted Screenplay nomination for "Sunset" in 2004.

The story of Jesse and Celine is one of the great romances in all of cinema, and one of Linklater's most significant accomplishments in a unique, rebellious career. The whole journey began on a train in 1995 with a couple arguing in German. That rocky relationship, which somehow seems perfectly stable despite the aggression and the fact that we have no clue what they're arguing about, fires an intriguing starting gun for three films that follow the progression of Jesse and Celine's love and lust and star-crossed passion over 18 years.

Indeed, by way of introduction at tonight's screening, Linklater offered merely, "We're all 18 years older now." And his films have been a brilliant gauge for tracking not only his characters' maturity, but his own development as a husband and a father. He read some sentiments from Hawke, who could not attend, which echoed that concept. "There is no place on Earth I would rather be than in Sundance tonight," Hawke wrote. "My theater schedule in New York has my feet tied, however. This premiere has been 18 years in the making. I remember vividly watching Mr. Redford introduce 'Before Sunrise' like it was last March. In many ways, it could be appropriate that I cannot make it to the screening tonight, as the star of this film is not Julie and me, but Father Time himself."

And so the tale comes full circle, as nearly two decades after their story served as the opening night presentation of Sundance 1995, we catch up with the couple nine years removed from the last time we saw them in Paris, Jesse on the verge of missing his flight but determined not to let this moment slip away a second time.

The new film, at a longer 108 minutes, was shot somewhat in secret in a remote area of Greece, and Linklater told the audience in a post-screening Q&A that that was beneficial. There were no expectations when they set out to make the first film. "We just made the movie," Linklater said. "It was a special, creative experience for us, to be sure. As the years went by we would get together, and it was a scary thought, to make the second movie. The second film, basically, no one wanted. Three people wanted it, Julie, Ethan and me. And I think because of the second film, it begged the question, 'Are you going to do another one?' So the low key was probably good to put all of that out of our mind and, again, to just do it for ourselves."

It would be wrong to reveal where Jesse and Celine are in their lives at the start of "Before Midnight," but it's a very natural place. Physically, they find themselves in Greece, but mentally, they find entirely new rhythms and the trio mine even deeper, more meaningful considerations of love, romance and relationships.

While "Before Sunrise" and "Before Sunset" have shown us beautiful slices of idealism in many ways, "Before Midnight" goes to darker places and reality is much more of a menace than it ever was. The film even spins its tires a bit, but that repetition is part of the point. We see them quarrel, an expansion on the mini-time bomb that went off in that cab in Paris nine years ago. And perhaps most profoundly, the film steers toward epiphany, but elegantly, truthfully, avoids it completely, never getting there.

This movie, particularly within the context of its predecessors, truly gets the progression of a relationship. And it gets that, most of all, that progression never has a destination. It is always in transit, rarely if ever reconciled. Love is a process.

Delpy was amazing in "Before Sunset" but she probably gives the best performance of the trilogy here. She's open, wounded, defiant, a truly remarkable creation. And Linklater lets the experience breathe a little more with some added characters in one sequence that are meant as a sort of framing with examples of relationships across a range of ages. But as ever, the magic of the story is when Jesse and Celine find themselves bouncing off of one another, soul mates turning up pay dirt in their thoughtful musings.

I will always love "Before Sunrise" because where Jesse and Celine are at that moment is a crystalline depiction of something you want to keep with you. It's romantic but not unrealistic. "Before Midnight" might be my second favorite as it goes deeper than perhaps any of the films, though that's not to take anything away from "Before Sunset," which is an important transitional moment for the characters (and frankly would have been a poignant ending had Linklater, Hawke and Delpy left it at that).

But what we ultimately get here is an understandable next step, an equally meaningful dissection and, in the end, a burning desire to see where they are in nine more years.