Riders of the West (1942)

In this entry of Monogram's "Rough Riders" series (no relationship to the dull TV series of the 50's), Ma Turner of Red Bluff sends for U.S. Marshal Buck Roberts to investigate a series of widespread rustling in the area. Town banker Miller, saloon-owner Duke Mason and the crooked sheriff are in cahoots with rancher John Holt, but they double cross and kill him. His son Steve witnesses the murder and kills the sheriff. Buck arrives and arrests Steve. Marshal Tim McCall, posing as an outlaw, gains the confidence of the gang and engineers the escape, with Buck's knowledge, of Steve from the jail. Sandy Hopkins, the third Marshal of the trio, poses as a peddler and learns that the gang intends to do away with Buck and rides to the Turner ranch to warn him. Red, a Turner ranch hand but also a member of the gang, overhears Buck telling Ma that Tim is really a U.S. Marshal, and he has Miller and Mason informed.