In 1870s Nevada, stagecoaches carrying gold shipments from the Comstock mines to San Francisco are repeatedly robbed by bandits who provide the driver and passengers with an elegant champagne picnic lunch while they haul away the loot. Having lost a fortune to the "Champagne Bandits," William Sharon, owner of the Golden State Bank, convinces Charles Crocker of the Central Pacific Railroad that the only way to defeat them is to build a railroad through the vulnerable, mountainous area between Virginia City and Carson City. After deciding that the man to build the railroad is engineer Jeff Kincaid, an adventurous and independent-minded fellow, they track him to a San Francisco jail, where he is being held for drunken brawling. After his bail is posted and he accepts the job, they send him to his hometown, Carson City. There he is reunited after ten years with his half-brother Alan and Susan Mitchell, his former childhood admirer who has grown into a beautiful woman. Both Susan and Alan work for her father Zeke, the editor of Carson City's newspaper, who fears that the railroad will bring riffraff to the peaceful town. Zeke commences an editorial campaign against the railroad that is supported by the stagecoach owner, Henry Dodson, who fears losing business, and surprisingly, by some mine owners, in particular Big Jack Davis, part-owner of the Golden Elephant Mine. Although Davis claims he is merely supporting his good friend Dodson, he is, unknown to all of them, the mastermind behind the "Champagne Bandits." Davis and his partner, Jim Squires, have been covering up the fact that the Golden Elephant no longer produces by pretending to ship out gold, then stealing everyone else's. While waiting for the arrival of automatic drills, the newest equipment for tunneling through mountains, Jeff and his crew begin dynamiting. Meanwhile, the freight wagon delivering the drills meets with an "accident" set up by Squires and the hired thugs who masquerade as miners. The wagon rolls off the mountain road, scattering equipment and killing the driver. However, when Jeff and his foreman, Hardrock Haggerty, search for salvageable equipment, they discover that before dying, the driver wrote a mysterious message, "S-O-U," in the dirt. Later, Zeke figures out that the driver may have been trying to spell out "Squires" and goes to the Golden Elephant to discuss his theory with Davis, who, without hesitation, shoots him dead. During the night, the thugs secretly return Zeke's body to the newspaper office, where Susan finds it the next day. Unaware of Zeke's discovery, Susan, Alan and others in the town suspect that he was killed because of his opposition to the railroad, and antagonism toward the railroad workers builds. A fight commences when the workers are refused service at the saloon, but Jeff stops it by challenging his own men. Alan, whose anger is fueled both by Zeke's death and by Susan's interest in Jeff, publishes anti-railroad articles and reports, unfairly, that the railroad men are terrorizing the town. After Susan declines his offer of marriage, Alan's jealousy keeps him from helping out when a landslide traps Jeff and several of his men in the half-built tunnel. After the townspeople, including Susan, help Hardrock and other railroad workers rescue the trapped men, Jeff and Hardrock discover that the landslide was deliberately caused by dynamiting. When the railroad is nearly completed, Davis, knowing he has been beaten, plans his last, most ambitious robbery. The train's initial run from Carson City to Virginia City carries an especially large gold shipment, as the mine owners have been waiting to deliver until the completion of the railroad. On board are leading citizens of both towns and Alan and Susan, who are reporting on the major community event. After watching the train leave the station, Jeff learns from Dodson that Davis has not been shipping out gold since railroad construction began. Knowing that Davis also did not ship out by train, Jeff proceeds to the Golden Elephant, where he finds champagne bottles and an unproducing mine. He captures the guard and with the help of his railroad workers, scares him into revealing Davis' plans. Meanwhile, on the train's return trip to Carson City, Susan and Alan also learn about Davis' plans. After highjacking the train, Davis' men stop it to unload the gold, but Jeff and his men show up and a shoot-out begins. After Davis and Squires escape with the gold, Davis kills Squires to avoid sharing the loot. Alan, who has pursued them, saves Jeff's life and then is also killed. Finally Jeff catches up with Davis, and after a fight, kills him. The rest of the phony miners are either killed or captured by Jeff's men. Later, while honeymooning with Susan in San Francisco, Jeff is offered a job by Crocker and Sharon to build a road linking Carson City to Reno.
