A crooked politician tries to stop construction of the first intercontinental railroad.

Bank president Asa M. Barrows stands to make a fortune if the Central Pacific Railroad reaches Ogden, Utah before the Union Pacific. Consequently, to prevent the Union Pacific from reaching Ogden first, Barrows hires gambler Sid Campeau to sabotage the railraod. Three years later, as the first engine, piloted by engineer Monahan, leaves Cheyenne, the Union Pacific hires trouble shooter Jeff Butler to keep order on the railroad. Jeff is faced with Indian raids and the corruption of the men by whiskey and gambling, all engineered by Campeau and his partner, Dick Allen. Dick and Jeff are old army pals who now find themselves fighting on opposite sides. They also find themselves in competition for the affection of post mistress Mollie Monahan, the engineer's daughter, who favors Jeff. When Campeau attempts to stir the men up over late wages, General Ulysses S. Grant coerces Barrows into lending money to the railroad. Barrows plans to recoup his loan by robbing the payroll train, and Campeau sends Dick to do the job. Dick steals the pay sack and rides off, followed quickly by Jeff. After hiding the sack in Mollie's mail car, Dick returns to retrieve it, only to find Jeff waiting. When Campeau and his thugs also appear, Mollie hastily accepts Dick's engagement ring in return for Jeff's safe passage, and insists that Dick give back the money. Jeff then leads his men to Campeau's saloon where, after extracting a confession from Campeau, they destroy the premises. Next, Jeff goes to the church to arrest Dick for the robbery, but arrives too late to stop the wedding. Mollie allows her new husband to escape and is fired by the railroad. The next morning, Dick appears to claim his reluctant bride, but his nuptial embrace is interrupted as the Indians attack and the train is derailed. Jeff, Mollie, and Dick, the only survivors, join forces to telegraph Cheyenne for help. As they fight for their lives, the troops race to rescue them, braving burning bridges to arrive in time. In the gunfire, Mollie is shot and Jeff allows Dick to escape. Before he leaves, Dick tells Jeff of Barrows' duplicity and promises to meet Mollie in Ogden. To reach Ogden in time, the railroad has to traverse a track built over snow, which collapses under the weight of the engine, killing Monahan. The engineer does not die in vain, however, for the Union Pacific thwarts Barrows and wins the race. As the last spike is driven, Dick is killed by Campeau, and thus, as all obstacles are removed from the union of the rails, so too are they removed from the union of Mollie and Jeff.