Hastening west with the information that will clear his brother's wife of murder, the last thing Deputy U.S. Marshal Kendrick Parker expects when he arrives in St. Louis is to come face to face with the notorious Black Bette Barclay. Knowing the San Francisco Marshal's office has a warrant for her arrest, Kendrick arranges to bring the dastardly woman as far as his brother's home in Adler Creek, Wyoming where he will turn Bette over to fellow lawmen. To avoid bringing undue concern to his fellow wagon train travelers, Kendrick concocts the story that Bette is his wife, Mandy.