Louis is August's father. He was in a band made up of all of his brothers and him. He was the lead guitarist and singer. After a gig, his brother's and him went out to a party, but Louis went to the roof to talk to the moon and listen to the music being played below by a man with a guitar and a harmonica.
While he was up there, a woman came out to escape the party. Her name was Lyla. He invited her up to the roof and after a little talking, they began to kiss. The next morning, Louis is woken by his brothers who spray him and Lyla with water. They are laying on a couch, all wrapped in blankets.
Lyla freaks out and explains that she needs to get home. Louis asks her to meet him under the arch at 10 and she smiles, which Louis takes as a yes. At 10, Lyla doesn't show and Louis books it across town to her hotel where he tries to catch her attention by calling her name. However, Lyla is ushered into a limo by her father and Louis doesn't see her again for eleven years.
After she's gone, Louis finds himself unable to sing anymore and he quits the band, leaving it one brother short and unable to continue. He'd been in the process of recording a song he'd written for Lyla after she left but couldn't bring himself to sing it.
Eleven years later, Louis is a businessman but finds himself unhappy with life. His brother invites him to his birthday party and Louis uneasily agrees to go. At the party, his brother's are showing a video of Louis singing at one of the band's gigs and the recording of the song Louis never finished.
Louis feels suffocated and pushes his brother, yelling at him until he gets punched in the face. Louis holds his face and then smiles thankfully at his brother.
Apparently, the party and the punch were enough to knock some sense into Louis and he quits his job, takes out his old guitar, and calls his brothers for a chance at getting the band back together. He even gets the manager of the place they used to play at to give them another shot.
Louis tries to call Lyla but she's not at her home in Chicago and he doesn't know where she is. Louis finishes the song he wrote for her so they can play it at their next concert. While he waits for his brother's to get there, Louis goes for a walk and sees a young boy playing a guitar in the park and looking lonely.
He puts some quarters in the boy's guitar case and greets him. The boy is August Rush, Louis's son through Lyla. However, August is an orphan and neither of them know their related, although they seem to have a connection.
Louis trades guitars with August and they have a nice guitar duet session and you discover that August and Louis have similar, but different, styles of playing guitar. When August is called away, Louis says goodbye and they trade back guitars so Louis can leave. Louis gives the boy one last curious look before they part ways for good.
Louis goes to his concert and performs the song he wrote for Lyla, enjoying himself for once. After the party, Louis is in a taxi with his brother's and headed for the airport when he spots a hanging advertisement for a concert being held in the park. He can hear it playing through the windows of the taxi.
They pass another one and he spots the names August Rush and Lyla Novacek on the banner and instantly forces his way out of the taxi. He desperately rushes to the concert in hopes of seeing Lyla there and finds August on stage giving an amazing performance.
Louis looks to his side and sees Lyla in the crowd. He takes a deep breath and follows her to the front of the crowd. While she's distracted by the child on stage, Louis slips his hand over onto hers and catches her attention. She smiles at him and he smiles back. Together, they look up at the son Louis doesn't know he has and watch him finish his composing. At the end of the number, August turns around and looks at them, both smiling up at him.