A mechanic alienates everyone who loves him when he becomes a champion race car driver.

In Carrell, California, Billy Coy, an aspiring race car driver, goes to Arthur "Red" Stanley's automotive garage and offers his services as a mechanic. After Red tells him that he is not hiring, Billy notices an autographed picture of the legendary driver "Cannonball" Coy, who was killed in a terrible accident during the Indianapolis 500, and reveals that he is Cannonball's son. Red, who used to be Cannonball's mechanic and clearly carries a torch for Billy's mother Mary, agrees to give the young man a job. On his way out, Billy meets tomboyish mechanic Louise, whose father, Reno Riley, owns the nearby racetrack. One day, Red allows Billy to drive one of his cars in a qualifying race, but the cocky Billy ignores his advice and spins out. Billy then asks Louise to meet him at the track Saturday night, and she gleefully assumes that he plans to take her on a date. When she arrives wearing a fancy dress and high heels purchased for the occasion, Billy explains that he was hoping she would help him install some carburetors, and Louise gamely conceals her disappointment. Later, Billy asks another owner, Deacon Jones, to let him drive in an upcoming race, but Deacon has already hired Happy Lee, another mechanic from Red's shop. In defiance of racing superstition, Billy accepts another owner's offer to drive a green car, which has been considered unlucky because Cannonball was driving a green car when he crashed. During the race, driver Vic Sullivan runs Billy's car off the track, but Billy walks away from the crash unscathed. Afterward, Happy burns his hand on an exhaust pipe, and Deacon agrees to let Billy drive the next race in his place. Billy wins the race, and when Happy recovers, they become Deacon's new racing team. One night, to celebrate his winning streak, Billy goes to a nightclub, has too much to drink and is arrested for speeding on the way home. The next day, Red bails Billy out of jail and advises him not to race that night, but Billy ignores him. During the race, Happy's wheel becomes loose, and Billy, pulling up close to his car, tries unsuccessfully to warn him. When the wheel flies off, Happy skids to a halt, and Billy is unable to stop in time and hits him. Happy is trapped in his burning car, and Billy cannot get past the flames to rescue him. Shunned by the other drivers and fired by Deacon, Billy decides to leave California. After promising Louise he will meet her at the Indianapolis Motor Speedway on Memorial Day, Billy goes East and gradually rebuilds his racing career. While he is gone, Red and Mary get married. One the day of the Indianapolis 500, Mary watches nervously from the stands as Billy races in Red's car. With only one lap left to go, Billy's engine catches fire, but he risks his life to continue driving. After crossing the finish line in third place, Billy jumps from the car just moments before the gas tank explodes. As Billy and Louise embrace, the winner of the race gives his trophy to Billy to honor him for his exceptional skill and bravery.