As dusk begins to deepen into night, two planes roar high over the shadowy range land of eastern California, and their flight marks the end of another dangerous adventure for Hop Harrigan and Tank Tinker, for now. In the lead plane, Hop is returning the wonder horse, Sequoia, to his rightful owner, the movie star Dixie Davenport, but unbeknownst to them, there is another plane flying above them, watching their every move...