Joanna O'Keefe sells off the family holdings in Texas to go find her husband in New Mexico Territory. He went with John McLeod dreaming of a cattle empire with millions of acres for the taking. On her way Joanna meets Angus McLeod bound to join his brother. When they arrive at the Circle MC they learn Alex has been murdered by unknown assailants. A young Mexican girl at the ranch is pregnant with Alex's child, and there seems no place for Joanna on the entire spread. The dream empire is further threatened by rising railroad cattle fees, and Joanna proposes an overland drive into San Diego. The route crosses the Colorado River and the Mojave Desert, and Joanna's determination proves her the equal of the men in the wild and rugged journey.