Ken McLaughlin (Roddy McDowall) is a precocious 10-year-old who lives with his family on a remote Wyoming ranch. When Ken returns home from school with failing grades, his father, Rob (Preston Foster), blames the boy's lack of personal responsibility. At the suggestion of his wife, Nell (Rita Johnson), Rob allows Ken to choose a single colt from the herd to raise as his own. Much to his father's dismay, Ken chooses a fiery mustang filly -- but the two soon become fast friends.