At the Scottsdale County Fair, Robert Bruce MacDougal offers Alonzo "Lon" Decker, a farm boy from Indiana, twenty dollars to ride his quarter horse, Jojo, in a match race. Despite the horse's unpromising appearance and his own lack of experience as a jockey, Lon accepts the offer, but Jojo throws him at the starting gate and is disqualified. The next day, at another fair, MacDougal is again using Jojo's seemingly inferior condition to set up match races at generous odds when Lon begs him for another chance. MacDougal slips the horse a pill before the race, and Lon rides Jojo to an easy victory. MacDougal and Lon's hasty departure arouses the suspicions of the other trainers, who are assured by the track steward that if the horse wins again under suspicious circumstances, the track officials will be ready to test the animal for drugs. As the racing season comes to a close, MacDougal offers Lon a job on his ranch, but Lon declines, explaining that he wants to study journalism and become a sports writer. Lon gives MacDougal his savings to bet on Jojo's last race, but MacDougal throws the race by giving the horse a sleeping potion. Afterward, Lon accompanies MacDougal to his dilapidated ranch, down the hill from the estate of wealthy Zelda Bagley. MacDougal carries on chess games through the mail with notable figures from around the world, and tells Lon he wants to acquire a thoroughbred in order to support this pasttime. One day, Lon meets Betty Richards, a portrait artist from Texas, who has been hired to paint a portrait of Zelda's new thoroughbred, Flyaway. Zelda calls on MacDougal, eager to acquire his land so that she can expand her training grounds, but MacDougal refuses to sell. Later, Betty tells Lon that she checked Jojo's brand and discovered that the horse is actually Texas Dandy, one of the greatest quarter horses in the country. After MacDougal watches Betty race his horse against Flyaway, he challenges Zelda to a match race at the upcoming Arizona State Fair, with his ranch and Flyaway as the stakes. Lon sells an article about Texas Dandy to a magazine, and he and Betty begin to discuss a future together. Suddenly, a bull jumps the fence, and while Lon is trying to corral it, Texas Dandy is gored. Citing a clause in his contract with Zelda that requires him to forfeit the match if he cancels for any reason, MacDougal insists on racing the injured horse, and reluctantly admits that he has been giving Texas Dandy drugs. Lon is angry and disillusioned, but when the magazine asks him to write about the race and MacDougal promises not to drug the horse, he agrees to stay and train Texas Dandy. On the day of the event, however, a nervous MacDougal gives the horse a pill, and although his wound reopens while he runs, Texas Dandy narrowly wins the race. The judges immediately conduct a saliva test, and MacDougal is amazed to discover that the pills, which he received from the horse's previous owner, are only aspirin. With his new horse Flyaway in tow, MacDougal departs for the racing circuit, leaving his ranch to Lon and Betty, who are now married and raising a new generation of quarter horses.