In 1995, Lyla Novacek (Keri Russell), a dedicated cellist at the prestigious Juilliard School, finds herself under the rigid control of her father. Meanwhile, Louis Connelly (Jonathan Rhys Meyers), the charismatic lead singer of an Irish rock band, crosses paths with her during an unexpected encounter on the roof of a party. Despite their mutual shyness, a spontaneous connection sparks between them, leading to a brief but passionate one-night stand. Unfortunately, Lyla's father forbids her from pursuing any relationship, severing their link.
Complications arise as Lyla discovers she is pregnant. Following a heated argument with her domineering father over her future as a mother, tragedy strikes when she is hit by a car, resulting in a premature birth. While Lyla lies unconscious, her father, Thomas Novacek (William Sadler), takes matters into his own hands and secretly puts their baby boy up for adoption, leading Lyla to believe her son has died.
Fast forward eleven years, the baby, now known as Evan Taylor (Freddie Highmore), resides in a boys' orphanage. He possesses remarkable musical talents, exhibiting savant-like abilities that set him apart, unfortunately also making him a target for bullying. Convinced that his parents will eventually find him, Evan escapes to New York City, determined to “follow the music” and uncover the truth about his origins. In a twist of fate, he disconnects from his social worker, Richard Jeffries (Terrence Howard), when he accidentally loses Jeffries’ contact number.
In Washington Square Park, Evan encounters a young busker, Arthur (Leon Thomas III), who leads him to a condemned theater where he meets Wizard Wallace (Robin Williams), an eccentric and overbearing street musician. Wizard mentors Evan and other kids in street performing, expecting them to share their earnings. When Evan impresses everyone with his guitar skills, Wizard dubs him "August Rush" and aims to capitalize on his talent.
As destiny unfolds, Louis has moved to San Francisco as a talent agent, while Lyla now teaches music in Chicago. Louis, feeling a deep longing, seeks to reconnect with Lyla after ending his relationship with his girlfriend, Jennifer (Becki Newton). On his way, Lyla receives devastating news from her father's bedside—her son is alive—which prompts her to search for him at all costs.
Louis’s attempts to locate Lyla lead him to misunderstandings that ultimately drive him to New York, where he reunites his band. As trouble brews, Jeffries grows suspicious of Wizard’s intentions and the authorities raid their hideout. During this chaos, Evan remembers Wizard's warning to never disclose his true identity, and he finds refuge in a church where he befriends a girl named Hope (Jamia Simone Nash). She introduces him to the piano, reigniting his passion for music as he forms a rhapsody that captures the attention of the church's pastor, Reverend James (Mykelti Williamson).
Driven by the need to find her son, Lyla visits Jeffries, who recognizes Evan as her long-lost child using vital information about his birth. As she practices her cello for a series of summer concerts with the Philharmonic in Central Park, August is selected to perform his original concerto during the same event. However, Wizard interrupts his rehearsal, claiming to be his father and trying to wrest control over August.
On the concert day, tensions rise as Wizard concocts a scheme to keep Evan from performing. In a moment of fate, Evan runs into Louis, who remains unaware of their familial connection. Despite his inner turmoil, August confides in Louis about his desire to take the stage. With Arthur's help, August manages to escape Wizard's clutches and races against time to make it to the concert.
Meanwhile, Louis, after playing with his band, spots Lyla's name on a concert banner and follows the signs to the park. Jeffries discovers an "August Rush" flyer and heads to the concert as well. Ultimately, as August conducts his much-anticipated rhapsody, he draws his parents to the audience. The performance culminates in a heartfelt reunion where August smiles, finally aware that his instincts about his family were indeed correct all along.
