Andy "Champ" Purcell, a former boxing champion, is idolized by his young son Dink, even though Andy's drinking and gambling have resulted in a childhood of cheap Tijuana hotels and pool halls for Dink. Because he loves the boy more than anything in the world, Andy tries to make one last attempt at a comeback, but alienates fight promoters when he shows up for a meeting drunk. Dink doesn't scold Andy, however, even though he knows that Andy's promises to change are meaningless. Some time later, Andy wins a racehorse and gives him to Dink, who calls him "Little Champ." They go to Tijuana to race the horse, and at the track, Dink meets Linda Carleton, a kind horse owner, and her wealthy husband Tony. When Tony runs into Andy at the track, he realizes that Dink is the child that Linda gave up when she and Andy were divorced many years before. When Little Champ falls down and loses the race, Andy is so desperate for money that he accepts Tony's offer of two hundred dollars to let Linda visit with Dink in her hotel. The next day, Andy dresses Dink in a new suit and takes him to Linda's hotel and waits outside while they talk. When Dink matter of factly tells Linda about his life with Andy, she determines to take Dink away from his father, even though the courts awarded him custody. The next night, while Andy gambles, Tony approaches him, asking if Linda can have Dink for six months to send him to a good school and give him the right environment. When Andy refuses, Tony threatens to take Dink away. Andy loses heavily that night and is forced to sell Little Champ, but promises the heartbroken Dink that they will get the horse back. With nowhere else to turn, Andy goes to Linda, who gives him the money, then begs him to let Dink decide if he wants to live with her or Andy. That night, instead of buying Little Champ back, Andy drunkenly tries to gamble "double or nothing" with the new owner and loses, then is arrested for starting a drunken brawl. Despondent over losing the horse and the money, Andy realizes that Dink would be better off with Linda and pretends that he doesn't want his son any longer. When Dink tearfully begs to stay, Andy hits him, after which Dink leaves and Andy repeatedly slams his fist against a wall as punishment for striking his son. Some time later, in Tony and Linda's private railroad car, the family travels toward New York. Still heartbroken over his separation from Andy, Dink decides to sneak out of the train when it reaches San Diego and goes back to Andy, who had been bailed out of jail by Tony. Andy is supposed to be in training for a new fight arranged by his friends Tim and Sponge, but is too despondent to train until Dink arrives. Now, hoping to be able to keep Dink for good, Andy trains vigorously and gives up drinking and gambling. His age and physical condition are against him, though, and Dink is worried that Andy will be hurt by the much-younger Mexican opponent. On the night of the fight, Tony goes to see Andy and assures him that he and Linda will not try to take Dink away again. Tony offers to help and tries to talk Andy out of the risky fight, but Andy insists that he will win and be able to care for Dink properly. During the brutal fight, when Andy is saved by the bell on a nine count, Dink, Tim and Sponge try to get him to throw in the towel, but Andy insists on one more round. Though exhausted, Andy comes back and wins the fight. After leaving the ring, however, Andy has a heart attack and dies in his dressing room. As Dink hysterically calls for "Champ," Linda arrives and comforts him as she carries him away in her arms.