Winter
The film opens with a traffic jam on an LA freeway. After the spectacle of the opening number ("Another Day of Sun"), we see barista and aspiring actress Mia going over lines for an audition in her car. She’s not concentrating on the road and so holds Sebastian—a jazz musician who dreams of owning his own jazz club—up. He beeps his horn loudly at her as he drives past. Mia’s audition is a disappointment, and she goes home to housemates who encourage her to join them at a party ("Someone in the Crowd"). The party is equally disappointing and, finding her car’s been towed away at the end of the night, Mia makes her way on foot, stopping on the way at Lipton’s restaurant, where a pianist is playing jazz. It’s Sebastian.
We hear the honking of a horn and the film replays this whole section, only this time from Sebastian’s perspective. Once out of the traffic jam, Sebastian makes his way to the Van Beek, a samba-tapas bar. Not to go inside, but just to stare at it—we later learn that the venue once housed wonderful jazz musicians and Sebastian dreams of setting up his own jazz club there, in honor of that history. But for now, he’s playing the piano at Lipton’s restaurant, and we see him with his boss, who is reminding him to stick to the Christmas set list (and specifically to cut out the jazz). But, after a few Christmas tunes, he veers off course and plays his own jazz music ("Mia & Sebastian’s Theme") as Mia is watching. She’s mesmerized and goes over to compliment him, just as he’s been fired. He brushes past her without a second look.
Spring
Mia’s at a pool party and goes over to where a 1980s pop cover band is playing. Sebastian is on keys and Mia mocks him for it. They end up walking back to their cars together. On the walk, they both acknowledge the wonderful night and agree it’s a shame it’s wasted on them—after all, they have no romantic potential ("A Lovely Night"). Sebastian tracks Mia down at her waitressing job and she tells him of her dream to be an actor and he tells her about his passion for jazz and takes her to a jazz club. Mia gets a call back for a TV audition and they’re both excited. She says the show’s like Rebel Without a Cause and so they decide to go to the movies together to see it. The call back goes badly and afterwards Mia has to go to dinner (a date she’s forgotten) with her boyfriend Greg and his brother and partner. Half way through the meal and alienated by the company, she makes her apologies and bolts, rushing out to meet Sebastian at the cinema instead. Their evening ends with a drive to the Griffin Observatory where they dance ("Planetarium") and finally kiss.
Summer
Mia is writing a one-woman show. Sebastian is playing in a jazz bar; Mia loves the music and dances along. There’s a montage of many happy scenes of them together ("Summer Montage"). In the jazz club, Sebastian is approached by Keith—an old friend and fellow musician—who offers him a job playing in his band. Sebastian declines. Mia finishes writing her one-woman show and tells her mother all about it, and about Sebastian who is "nobody yet" but dreams of owning his own club. The truth of the comment hits home for Sebastian and he takes the job with Keith. The band is called The Messengers and they play a huge concert which Mia attends ("Start a Fire").
Fall
Mia invites people to her one-woman show, So Long Boulder City, while Sebastian is on tour. She hasn’t heard from him for a while, and when he does show up, having made a home-cooked meal as a surprise for her, they fight about how long he plans to be away. She reminds him that he was supposed to be saving up to own his own club, not committing to the band indefinitely. On the night of Mia’s performance, Sebastian is held up at a photoshoot. After this, Mia breaks off the relationship, saying she’s going to move back to Boulder City and give up acting. A casting agent contacts Sebastian, looking for Mia—they saw her show and want to call her in for a film audition. Sebastian tracks her down in Boulder City and drives her to the meeting, where she simply has to tell a story. Afterwards, Sebastian and Mia discuss their future and decide they should each follow their own paths and see what happens. After all, if Mia gets the film she’ll be in Paris for months…
Winter
Five years later and Mia is a successful actress and is married, but not to Sebastian. She has a daughter and a happy home. On a night out with her husband, the pair get stuck in traffic on the freeway, so they detour—to a jazz club, called Seb’s. Sebastian and Mia meet again, and he plays their love theme ("Epilogue"). As he does, she imagines the life they might have had together and, leaving with her husband, exchanges a last look and a smile with Sebastian.
