Alex O'Keefe left Texas with John McLeod, who had fired him up with dreams of an empire and millions of acres for the taking in New Mexico Territory. Surrendering to her husband's enthusiasm, Joanna O'Keefe sells out the family holdings and boards a train to join him. On the way she meets Angus McLeod, bound to join his brother. On arrival, Joanna finds Alex has been murdered, and what's more, there is a young Mexican woman carrying his child...But Joanna has nowhere else to go. Then the dream empire is threatened when the railroad raises cattle fees higher than their sales would bring. It's Joanna who proposes an overland drive into San Diego, across the Colorado River and Mojave desert, proving herself as capable as any of the men in that wild and rugged terrain.