It's about the construction of the Union Pacific Railroad, the eastern half of the Transcontinental Railroad which formed the first rail link between the eastern and western halves of the United States. The film opens at the end of The American Civil War as Congress authorizes a transcontinental railroad. The law provides for the Union Pacific Railroad to build from the east and the Central Pacific Railroad to build from the west.
A corrupt businessman named Barrows (Henry Kolker) sees a means to profit off of this plan. While pretending to invest in the Union Pacific he secretly backs its rival, the Central Pacific. He then hires a slimy gambler, Sid Campeau (Brian Donlevy), to basically bring along with the railhead a portable Red Light District filled with saloons and prostitutes and the like. Sid's job is to retard progress on the railroad by distracting the workers with his liquor and whores, and to use more direct means if necessary. This will allow the Central Pacific to make more progress and to reach the vital junction of Ogden, Utah before the Union Pacific does.
Enter "chief troubleshooter" Jeff Butler (McCrea). Jeff is hired by the Union Pacific to basically be railroad law enforcement, maintaining order to keep the workers from being distracted and to facilitate the progress of the railroad. He immediately runs into conflict with Campeau. This conflict is complicated by the presence of Mollie Monahan (Stanwyck), the engineer's vivacious daughter. Molly has sparks with Jeff but has another suitor in the person of Dick Allen (Robert Preston), Jeff's old war buddy and one of Sid Campeau's mooks.
A young Anthony Quinn has a small part as one of Campeau's goons.
- Artistic License – History:
- The opening scenes with the political maneuvering around the railroad are mostly nonsense. There was hardly any opposition to the idea of building a railroad, and in fact engineers had been scouting routes ever since the United States stole what is now the American Southwest from Mexico in the Mexican-American War. The conflict was over where to build the railroad, with the southern states insisting on a southern route. After the South seceded from the union, the remaining states passed the Pacific Railroad Act in 1862, three years before the end of the war.
- Also, having a congressman say the west coast had no harbors was ridiculous, since the capacity of San Francisco Bay as a gigantic natural harbor had been known for nearly a century and was one of the reasons the United States invaded Mexico to begin with.
- As You Know: Grenville Dodge is addressed with "General Dodge, as chief engineer of the Union Pacific railroad..." when asked a question.
- The Big Board: Dodge has a map hanging in his car where he tracks the progress of both railroads. He is unhappy about the Central Pacific getting ahead of them in the race for Ogden.
- Blowing Smoke Rings: Dick unwinds while conspiring with Campeau, while plotting a fake robbery of Barrows' money, via a weird variant on this trope. He has made a box out of playing cards. He blows cigar smoke into the box. He taps on the box, and smoke rings come out of a hole in the side.
- Brick Joke: Barrows is punished for his evil machinations by being forced, at the point of a gun, to go down a very long stretch of track whacking spikes with a slegehammer. He is exhausted and bedraggled when he is finally released—but at the end, when he's asked to drive home the ceremonial spike at Promontory, he swings the hammer with style and slams it in.
- Death of the Hypotenuse: The movie needs Jeff and Mollie to get back together at the end, but unfortunately Dick is still married to her. So Campeau shoots Dick to death during the climactic confrontation at Promontory, Utah.
- Desert Skull: The aridity of the Great Basin is underlined by the cow skull and spinal column seen by the tracks in one shot as the train chugs west.
- The Film of the Book: Adapted from the 1936 novel Trouble Shooter by Ernest Haycox.
- Gold Fever: Cleverly exploited by Jeff. The train is about to move out of camp for end of track, but most of the workers are still in Sid's saloon, drinking, gambling, and whoring. So Jeff gets Leach to pull his lucky charm gold nugget out of his pocket, then loudly questions him about it while suggesting he found it at end of track. The workers overhear, get excited about gold, and hop on the train, to Sid's fury.
- Injun Country: The train is attacked and derailed by a party of Sioux. The racism of this is somewhat lessened by how the film makes clear that Red Cloud and the Sioux had made peace with the railroad, and how the peace was broken when Campeau's goons shot and killed a Sioux brave for sport. And the scene is possibly justified by how a party of Cheyenne actually did derail a Union Pacific train in Real Life in 1867. But the racism is ratcheted right back up when the Sioux put ladies' underwear on their horses and do stuff like goggle in shock at a wooden Indian and a piano.
- It Will Never Catch On: A congressman confidently asserts that a transcontinental railroad is pointless and will serve no purpose as it will go through empty prairie and desert to a west coast with no harbors.
- The Mole:
- Barrows, who is posing as an investor with the Union Pacific while actually being far more invested in the Central Pacific, and while scheming to undermine the Union Pacific from within.
- When Dick has to go on the run, he suggests going to help the Central Pacific the same way he "helped" the Union Pacific.
- Off-into-the-Distance Ending: Ends with a shot from the modern day of a train zipping off into the distance.
- Opening Crawl: The opening credits are presented this way, to conform with the opening image of a railroad extending off to the far horizon. Contrary to other examples of this trope, the exposition that follows the credits is shown as a regular title card.
- Poor Man's Porn: Campeau is seen reading a Police Gazette in his first scene.
- Pretty in Mink: Mollie is impressed when Dick presents her with a fancy fur coat.
- Railroad to Horizon: The opening credits are played over a shot of a railroad extending off to the horizon, evoking the image of the Union Pacific headed off to the west.
- Time Skip: After the passage of the railroad law and Barrows' deal with Campeau, three years are skipped, moving the story to 1868 and finding the Union Pacific in Wyoming and struggling to reach Ogden before the Central Pacific does.
- The Voice: President Abraham Lincoln is heard in the first two scenes in Washington, but never appears apart from a hand signing a bill.