Over breakfast one morning at his wife Alice's family ranch in California's Salinas Valley, Fred Tiflin informs ranch hand Billy Buck that he is going with him to an upcoming auction to ensure that he stays sober and on time. Fred, a former schoolteacher, then complains to Alice that their young son Tom is spending too much time on ranch business and not enough on his studies. Tom, meanwhile, asks Billy, a horse expert, if he can borrow the newspaper clipping about a race that Billy's mare Rosie recently won, as his schoolmates do not believe him. On his way to school, the impressionable Tom, who daydreams about knights in armor and circuses, shows the clipping and Rosie's blue ribbon to his friends and hints that Billy may give him the colt that Rosie is carrying. Later, Alice's father, a former wagon train leader who loves to reminisce about the "westerin'" years, returns from a hunting trip. Fred and Billy then return from the auction, and after dinner that night, Fred presents Tom with a red pony he bought while away. Thrilled by his new responsibility, Tom names the horse Gabilan and gratefully accepts a show saddle from Billy. Although Billy warns Tom that Gabilan will not be strong enough to hold his weight for some time, Tom persuades Billy to help him begin training the young pony right away. Unaware that Billy is instructing Tom, Fred, who has a respectful but distant relationship with his son, offers to help him with Gabilan and is hurt when he realizes that Tom has turned to Billy. Fred then rails against his self-centered father-in-law for telling his wagon train stories over and over, and a chagrined Grandfather apologizes. Ashamed by his outburst, Fred suggests that he and Alice leave immediately for the upcoming homecoming celebrations in his home town of San Jose, but Alice, who knows that Fred feels out of place at the ranch, suggests that he go alone to "think things through." Some time later, Tom brags to Billy about how much he has taught Gabilan and shows him how the pony can open the stable door with his mouth, a trick that gives Billy cause for concern. One morning, after a wet night, Tom makes Billy promise to put Gabilan away if it begins to rain again and heads off for school. A few hours later, the rain starts, and, as promised, Billy puts Gabilan into his stable. As soon as Billy goes back inside, however, Gabilan opens the stable door and wanders into the yard. Tom, meanwhile, is unable to concentrate in school out of worry for Gabilan and races home. To his dismay, he finds Gabilan standing in the heavy rain and accuses Billy of breaking his promise. Denying Tom's charge, Billy examines Gabilan and determines that he has contracted a case of "the strangles," a disease in which an overproduction of mucus blocks the horse's windpipe, leading to suffocation. Having been wired by a concerned Alice, Fred finally returns from San Jose, but tells Alice that he is considering taking a permanent position in the city. Soon after, Billy is forced to lance a lump that has developed on Gabilan's neck and consults with Grandfather and Alice about cutting a hole in Gabilan's windpipe to allow air into the pony's lungs. The normally confident Billy then reveals to Alice and Grandfather his distress that Tom still does not believe that he put the pony in the stable during the storm. Later, Tom is traumatized to see Billy cut the hole in Gabilan's windpipe. When Gabilan's end appears imminent, the adults gather at the breakfast table and decide not to try to shield Tom from the reality of death. Before dawn the next morning, Tom, who has been sleeping in the pony's stable, awakens with a start and, seeing Gabilan gone, rushes outside. Frantically following the pony's hoofprints, he finds the spot where Gabilan chose to die during the night. When Tom sees a flock of vultures gnawing on Gabilan's corpse, he is thrown into an hysterical rage. Tom fights with one of the birds and is about to kill it when he is stopped by his father and Billy. Despite Billy's attempts to console Tom, the boy remains disconsolate, even when Billy promises him Rosie's colt. Later, in the middle of night, Billy awakens and searches for Rosie, certain that she is about to deliver. He confides to Grandfather that he has had a dream that the colt has become caught in the breech position in Rosie's womb. Determined to deliver it for Tom's sake, Billy sharpens his knife, ready to sacrifice his beloved Rosie to ensure her unborn's safety. Having eavesdropped on Billy and Grandfather's conversation, Tom, who has since come to terms with Gabilan's death, sneaks into Billy's room and steals the knife. Fred, meanwhile, also wakes up, and informs Alice that he now knows that he has been a stranger to everyone but is ready to make the ranch his home. Billy then catches Tom with his knife and grabs it from him, but Tom follows him to the stable and screams for him to stop. When they all reach the stable door, however, they are surprised and delighted to see a healthy colt struggling to stand at its mother's feet.