The Lone Hand(1953)

Cowboy star Ken Maynard is Jim "Trigger" Morton, in town undercover while pursuing the man who framed him for robbery. But a well-placed shot tames a band of scofflaws and gains Morton the sheriff's badge. Now, he's riding on both sides of the law. The line is further blurred when old buddy Chuck offers evidence of Morton's innocence in exchange for a blind eye to Chuck's impending postal heist in this classic Western.

John Martin is a government agent working under cover. Leading citizen Morgan calls in gunman Galt who blows Martin's cover.

Johnny Mack Brown and Raymond Hatton return to the screen as saddle pals Nevada and Sandy in Monogram's Pals of the Border. In this one, our heroes are US marshals, hot on the trail of cattle rustlers.

Hoppy goes undercover as a gambler from the East when Bar 20 cattle are stolen by unknown rustlers. Brennan/Talbot are twin brothers (one a casino owner, the other a rancher) and Hoppy believes they provide alibis for each other while one is out committing crimes. Hoppy gets a job in the casino to learn more but is exposed when a gambling gunslinger notices him.

Summarily accused of murder, drifters Duke (Foran), Pancho (Carrillo) and Andy (Devine) are tossed into the hoosegow, only to be released when their alibi checks out. Far from offended by his ill treatment, Duke agrees to take the job of sheriff, retaining Pancho and Andy as his deputies. The gruesome threesome then sets about to solve a series of mysterious Wells Fargo robberies

The earliest surviving film featuring Lon Chaney in a major role, By the Sun's Ray's was but one of several 2-reel westerns starring the florid Murdock MacQuarrie. MacQuarrie plays a detective investigating a series of gold shipment robberies. Along the way, he falls for a mine superintendent's pretty daughter (Agnes Vernon), much to the dismay of a sullen mine office clerk (Chaney), who is also smitten with the girl...

Major Lex Kearney, dishonourably discharged from the army for cowardice in battle, volunteers to go undercover to try to prevent raids against shipments of horses desperately needed for the Union war effort. Falling in with the gang of jayhawkers and Confederate soldiers who have been conducting the raids, he gradually gains their trust and is put in a position where he can discover who has been giving them secret information revealing the routes of the horse shipments.

A reporter goes undercover to break up an outlaw gang.

Tex Weaver is working under cover to bring in a gang of bank robbers. When he is killed, Tim Ross, a marksman with Doc Shaw's traveling show, takes over. Posing as a Mexican he lays a trap for the gang.

Bill Tracy is a Cattleman's Protective Association agent. Working undercover on his way to Sonora, a town dominated by rustlers, saves Betty Carter from a situation, but her rancher father, believing Blackie's suggestion that Bill is a rustler, forbids her to see him. Bill and his pal Heinie Schmaltz rescue each other from rustlers' various plots and ambushes and eventually discover that Blackie, Carter's foreman, is the leader of the rustlers.

When one of Europe's most lethal terrorists shows up in New York, an elite undercover cop is assigned to take him down by any means necessary.

Red is an aging scam-artist who's just been released from prison together with Ronnie, a young and not-so-bright hoodlum who is easily manipulated. Their new business is to organize fake-money sales and then kill the buyer to take his money; but when Ronnie kills an undercover secret service agent, his partner Jimmy Mercer vows revenge and is given one week to catch the killers before being transferred.