Katy is the only daughter of a rancher who hopes to take over the family ranch someday. Her father, however, hopes that her older brother Howard will take over the running of the ranch. After failing to complete an essay for her high school exam, Katy returns home for the holidays to face her father's disapproval. Her redemption comes in the form of a black Mustang filly which Katy encounters after a close call with a mountain lion. Katy sets out to capture this Mustang who she names Flicka in an effort to prove to her father that she is capable of assuming the responsibilities of running the ranch. Katy's father does not approve of her actions, however, and after Katy deliberately disobeys him by training and riding Flicka behind his back, Flicka is sold to the rodeo for use in the wild-horse race. Katy succeeds in rescuing her beloved horse with the assistance of her brother by posing as a man and entering the race, she then takes Flicka and rides towards home. Another encounter with the mountain lion on the way back to the ranch results in Flicka being critically injured and Katy becoming seriously ill after being caught in a major storm. Her family find her and take her home while her father returns to put Flicka down due to the seriousness of her injuries. Katy hears a gunshot whilst she is battling the fever and assumes Flicka has been killed. A few days later, Katy's fever breaks; however, she is depressed at her horse's assumed death. Katy's father calls her downstairs and into the yard where Katy discovers that Flicka is alive and well, the shot she had heard was aimed at the mountain lion. The film ends with Katy and Flicka riding together through the Wyoming mountains.