"She-Wolf of the Rio Grande" opens to a band of nocturnal riders, rustlers from the wilds of Chihuahua who have crossed the border to drive off a herd of cattle belonging to Ross Millerick's Block M. They are led by a woman wearing a black leather mask. To her men she is known as The Angel. To those who fear her she is called Hija de Satan s, Daughter of Satan. Ross Millerick has enlisted the help of Texas Ranger Tom Garrett, who gives pursuit across the Rio Grande into Mexico where he has no authority but discovers that The Angel may be more sinned against than sinning.