Riding Midnight on a deserted road at the edge of town, Jed is accosted by a desperate gunman determined to steal his horse. Drew Bryant, a young rancher passing by, uses a make-believe “gun” to disarm the bandit and save Jed’s horse.
 
Jed’s Pa decides to invest heavily in a new railroad venture. When the fledgling company goes out of business, Pa loses his wealth and his home, Meadow Green. Angry at God and feeling that he has failed his family, Pa plans a quick trip to the Dakota Territory to visit a rancher friend, Hank Higgins. Jed and Nathan beg to be included in the trip, and Pa reluctantly agrees.
 
After a grueling journey by stagecoach, the Cartwrights arrive at the Diamondback Ranch only to learn that the ranch has been hit repeatedly by rustlers. When the ranch hands find scores of Diamondback cattle dead, they realize that the rustlers want more than cattle – they are trying to drive the Higgins family from the ranch.
 
Why are the rustlers do determined to steal the Diamondback? Is Drew Bryant involved with the rustlers? What is the secret of Diamondback Ranch?