The Road Demon.

Tom Mix trades horses for cars. Tom Higgins meets Patricia O'Malley whose father is a car manufacturer. O'Malley is hoping to land a contract with a Japanese firm, if only his car wins the Los Angeles-Phoenix auto race. Hap enters, but O'Malley's driver, Luther McCabe causes the race to be lost. Higgins discovers that McCabe is in league with O'Malley's competition, so for the next race, in Fresno, he takes over when McCabe drops out and wins the race.