At the Winfield Hatton Mining Enterprises in Cripple Creek, Colorado, a witness testifies to company representative James Sullivan and Marshal John Tetheroe about the latest in a series of gold ore shipment robberies. Due to the nation's low gold reserve and an embargo on gold shipments abroad, the Secret Service becomes involved in the investigation and Western division chief William Drummond assigns agent Bret Ivers to go undercover, posing as an outlaw fleeing Texas. At the Texas-New Mexico border, Drummond and Larry Galland, Bret's frequent partner, rendezvous with Bret. Drummond tells them several government agents have already died attempting to discover not only who is stealing the gold ore, but how it is being used. Larry's brother Strap, going under the name Gillis, is already in Cripple Creek, watching the ore's transport company, the Cabeau Liberty stable, which is run by Emil Cabeau. Bret and Larry ride into Cripple Creek and head for the local saloon, where Strap works as a card dealer. Shortly after Bret and Larry settle in, Larry recklessly comes to Strap's aid during a holdup, but Bret uses the opportunity to ask the saloon's owner, Silver Kirby, for work. Tetheroe, who is actually in league with Kirby, suspects that Bret and Larry know Strap and sends to Texas for information about them. Later, Strap informs Bret and Larry that he suspects Kirby is behind the thefts and that Cabeau works for Kirby. He is uncertain whether saloon hostess Julie Hanson's father Hardrock, an old-time prospector, is involved. That night, Bret and Larry stake out Cabeau's and follow his ore-laden wagon, which meets a second wagon and splits its load. Bret and Larry then steal the ore and dump it in an abandoned mineshaft that used to belong to Hardrock. At the saloon, Cabeau recognizes Bret, who admits they stole the gold, not realizing it was Kirby's. Kirby then insists Cabeau hire Bret and Larry to keep an eye on them. A few days later, Tetheroe receives a letter from his confidante in Texas, who reveals that an unnamed outlaw is suspected of being connected with the government due to his inexplicable release from jail. Unable to locate Kirby, Tetheroe leaves the letter with the saloon cashier as Strap checks in his chips. Strap steals the letter just before Kirby returns and rides after Tetheroe, who is supervising another ore transport with Cabeau, Bret and Larry. Strap tells Tetheroe that Kirby has read the letter and wants to see him immediately. Secretly, Strap slips the letter to Bret, adding that as he must be under suspicion, he will withdraw from the investigation. While riding back to town with Tetheroe, Strap attempts to arrest him, and in the ensuing gunfight, the marshal is killed. While Kirby and his henchman, Denver Jones, are looking for the letter, they intercept Strap and force him back to town. Meanwhile, Cabeau sends Bret and Larry away to keep them from learning the ore's final destination, but the pair double back and follow Cabeau to a deserted but functioning silver mine. At the saloon, Kirby tortures Strap to confess that he is the government spy but learns nothing. Jones then cold-bloodedly shoots Strap in the back and when Bret and Larry return, informs them that he has killed Strap, hoping to provoke a response. Later, Bret and Larry see Hardrock leaving town and, knowing he has witnessed some of the ore transports and certain that he is not involved with Kirby, follow him. Bret tells Kirby he has "kidnapped" Hardrock to keep him out of the way, which impresses Kirby and placates Julie. While Larry keeps Hardrock at a rundown cabin near the mines, Bret returns to the silver mine and, sliding down the shaft, watches as a number of workers melt down the gold ore into bars and coat them with lead before packing them in crates bound for Peking, China via Denver and San Francisco. To protect Hardrock, Bret instructs Larry to take him to Denver before going on to San Francisco following the shipment. Larry then intercepts a letter from the Chinese shipper to Ah Fong, Cripple Creek's laundry man. While Bret waits for Larry's return, Jones discovers that the Texas letter was about Bret and informs Kirby that Bret and Larry must be the government agents. Kirby picks up Larry on his way back to Cripple Creek, but Bret breaks in just as Kirby begins torturing Larry for a confession. After a brawl breaks out in the saloon, Kirby escapes and Bret and Larry subdue Jones and the other henchman, who are turned over to Hatton and local lawmen. Bret and Larry rush to Ah Fong's, where they find Julie paying off Sullivan, who admits he is half Chinese and that he masterminded the thefts to help pay for a revolution in his country. Kirby bursts in with his gun drawn, but Bret shoots him as Julie breaks down and confesses that Kirby was her husband. With the ore ring broken, Bret and Larry depart Cripple Creek.