Adapted from a novel by Frederick Hazlitt Brennan, a race horse is bought and sold, treated well and badly, but is rehabilitated to win the Kentucky Derby despite a handicap.
On a horse farm MacGuire (J. Farrell MacDonald) wants to buy a horse from Jim Rellence (Ernest Torrence). In the rain pregnant Southern Queen gets stuck in the mud, has a foal, but must be shot. Uncle Ben (John Larkin) and his family care for the colt. Jim has Sammy (Eugene Jackson) give Tommy Boy a wet nurse. Jim finds that Tommy Boy can run but tells Hartwick (Harry Holman) that he isn't much. Hartwick looks at Tommy Boy and buys him for $6,000. At Latonia racetrack Tommy Boy wins. Angela (Marie Prevost) gets her husband Ludeking (Hallam Cooley) to buy Tommy Boy for $40,000. The trainer says Tommy Boy is not ready after the journey, and he loses.
Rid Riddell (Clark Gable) deals blackjack, and Tip Scanlon (Lew Cody) tells Ruby (Madge Evans) to stay away from Rid. Ludeking tells Tip to stop his wife's credit, and he sells Tommy Boy for $20,000. Rid kisses Ruby, but she warns him about Tip. Rid advises Tip not to run Tommy Boy. Ruby drinks because of Rid. Tip has a pill given to Tommy Boy and wins $25,000 on him. Tip tells gamblers to bet on Tommy Boy. Rid tells Tip that he objects to drugging Tommy Boy and warns he is tired. Tommy Boy loses, and Tip quickly packs, giving the horse to Ruby; but in the hall Tip is shot. Ruby asks Rid if he would race Tommy Boy honestly, and he says no.
Ruby gives up drinking and takes Tommy Boy to Jim Rellence for training. Rid arrives and finds Ruby healthy and happy. She says she entered Tommy Boy in the Kentucky Derby. Celebrities attend at Churchill Downs. Frazier has a horse entered and learns that Tommy Boy is the horse to beat. Jim says he never bets but puts money on Tommy Boy. Uncle Ben tells Ruby that Frazier has got the jockey to pull back Tommy Boy; but they plan to prevent it by filing the bit. In the race the jockey pulls back Tommy Boy until the rein breaks. Then Tommy Boy wins the Derby. Rid congratulates Ruby, who rejects him. Uncle Ben tells Ruby that he promised Rid he would not say that Rid tipped him off. Ruby goes to Rid, and he offers her a new deal as they embrace. Uncle Ben talks to Tommy Boy.
This dramatic story of a thoroughbred gives us the horse's point of view and realistically portrays a family of black servants on a horse farm. These natural elements are contrasted to the artificial world of gambling and greedy crooks.