Trying to make ends meet, Joan Prescott contracts to sell her horses to the U.S. Army, for which Captain Hartford is acting as agent. During the negotiations he casts suspicion of working with below-border revolutionists on Tom Rankin, ostensibly a wrangler. However, after Rankin recovers the stolen horses, he exposes Hartford and a Secret Service agent as rustlers and reveals his own identity as the real Captain Hartford. More on Wikipedia or Mubi
Watch Under Texas Skies (1930)
