Speed Racer, portrayed by Emile Hirsch, is an 18-year-old with a passion deeply rooted in automobile racing. His parents, Pops (John Goodman) and Mom (Susan Sarandon), manage the family-run Racer Motors, alongside his little brother Spritle (Paulie Litt), mechanic Sparky (Kick Gurry), and his girlfriend Trixie (Christina Ricci). As a child, Speed looked up to his older brother, Rex Racer (Scott Porter), a record-breaking racer whose life tragically ended during the Casa Cristo 5000, a challenging cross-country rally. Now, Speed is eager to carve his own path but remains dedicated to both the sport he loves and the well-being of his family.
The wealthy E.P. Arnold Royalton (Roger Allam), who runs Royalton Industries, offers Speed a lavish lifestyle in exchange for joining his racing team. Speed is initially tempted but ultimately refuses, motivated by his father's skepticism about corporate greed. In a fit of anger, Royalton exposes the dark truth about the racing world—key races are rigged for profit, including those involving Royalton himself. Seeking revenge, Royalton sends his drivers to wreck Speed's Mach 6 and subsequently sues Racer Motors for intellectual property theft.
In a twist, Inspector Dectector (Benno Furmann), who heads a corporate crimes division, presents Speed with an opportunity to fight back. Racer Taejo Togokahn (Rain) claims to have incriminating evidence against Royalton but insists that Speed and the enigmatic Racer X (Matthew Fox) race for him in the Casa Cristo 5000. Earlier, Racer X had saved Taejo from the notorious race fixer, Cruncher Block, who had planned to kill him when his attempts to rig a race failed. Taejo's motives for racing become clearer—victory would boost his family's business and thwart a buyout orchestrated by Royalton.
Despite his family’s lack of knowledge about his decision to race, Speed accepts the challenge, and Inspector Detector’s team modifies the Mach 5 to enhance its performance for the rally. As they train, Speed begins to suspect that Racer X might secretly be Rex. Unbeknownst to him, his family eventually learns about his participation and eagerly supports him. With Trixie and his family’s help, Speed battles through a host of ruthless competitors bribed by Cruncher Block, overcoming tremendous obstacles to secure victory.
However, Taejo's intentions are revealed to be selfish when he disregards the evidence against Royalton, leading to an intense confrontation between Speed and Racer X. The masked Racer denies being Rex, insisting that his brother is indeed gone. Back home, Speed receives an invitation for the Grand Prix from Taejo's sister, Horuko Togokahn (Yu Nan), prompting the Racer family to build a new Mach 6 in a staggering 32 hours.
As Speed enters the Grand Prix, he faces significant challenges—Royalton has put a bounty on his head, and he must compete against renowned driver Jack "Cannonball" Taylor (Ralph Herforth). After a slow start, Speed uses his wits to expose Taylor's cheating methods during the race, ultimately leading to Taylor's crash. Speed achieves triumph, uncovering Royalton's corrupt practices in the process.
In a poignant flashback, it is revealed that Racer X is indeed Rex, who has faked his death and altered his appearance to protect his family and the sport he loves. Consequently, he chooses to remain anonymous, believing this is the only way forward. The Racer family rejoices in Speed's hard-fought victory, while Speed and Trixie share a sweet moment and Royalton faces justice in prison.
