This surprisingly violent 15-episode serial takes place on the border between Texas and Mexico. When warned by Captain Jack of the Texas Rangers of impending trouble, elderly rancher Bill Burrel swears that Mexican cattle rustler Pancho won't do any riding or shooting in the area again. Pancho's lieutenant Santas, (who desires his boss's daughter Juanita's hand, and has been refused), overhears Burrel and decides to make things rough on Pancho by stirring up trouble for both sides. Pancho and his raiders, sworn to drive the settlers off the border country, attack the Burrel ranch and shoot Burrel dead, and his son Harry swears to make Pancho pay for his night's work. In the conflict that follows Pancho is knocked unconscious and his hands crushed in a press by masked men, apparently Texas Rangers. Though the torture is actually performed by the traitorous Santas and his cohort Rodriguez, Pancho blames the Rangers for the injury, swears revenge, and the two factions resolve to destroy each other. In succeeding chapters, Pancho and his ruthless gang menace Harry, his sweetheart Ruth and abduct Harry's younger sister Blanche, inflicting fiendish and deliberate tortures upon them. Pancho's demands are carried to his sworn enemies by the black-garbed "emissary of evil" the Masked Rider, who rides onto the scene without warning to kidnap, assault, or fire upon the Texas Rangers, their relatives, and even their horses. Pancho's daughter Juanita, frequently harassed by his men, is shocked by her father's cruelty and takes surreptitious action to prevent his murdering innocent captives when she can. She also falls in love with Captain Jack of the Rangers, which complicates matters even further. Rugged and outspoken "Ma Chadwick," Ruth's mother, helps the Rangers when Blanche and then Ruth are both kidnapped. Interesting shooting locations include a hacienda complex in Sabinas, Mexico, an ancient mission in San Antonio, the gigantic Medina Dam, at which a terrific action sequence was apparently almost thoroughly improvised (the scene does not appear in the original shooting script), and the "hole in the wall," a labyrinthine passage through the border mountains.