Wyoming ranchers Rob (Preston Foster) and Nell McLaughlin (Rita Johnson) somewhat reluctantly decide to give their 10-year-old son, Ken (Roddy McDowall), a chance to raise a horse and learn about responsibility. He chooses a one-year-old filly and names her Flicka, which ranch hand Gus (James Bell) informs him is a Swedish word for "girl." Rising debts and a "loco" strain have created problems for the McLaughlins. They accept a $500 offer from a neighboring rancher for the young filly's mother, Rocket, but the mare is accidentally killed while she is being loaded into a van.

The situation gets worse when Flicka is badly cut by barbed wire and the wound becomes infected. Ken cares for her best he can, but the infection leads father Rob to conclude that the horse must be put down. A gunshot by his father makes Ken fear the worst, but it turns out he was warding off a mountain lion after being warned by Flicka. The filly's life is spared, and young Ken nurtures her back to health.