In the Ozark Mountains of Missouri, outlaw Jim Plummer holds a party to celebrate his forthcoming marriage to Kate Foley. Meanwhile, on the road to Jim's place, Kate's mother begs her not to marry the outlaw. When Kate insists that she will go through with the marriage, even though she does not love Jim, her mother refuses her blessing and leaves her daughter to continue alone. Along the road, Kate is met by Ed Bagley, one of Jim's men. Bagley shows her a letter from Winnie McPhail, a former resident of the area, who now lives in the gold mining town of Bannock City, Nevada. The letter reveals that Jim's brother Frank, who now goes by the name Frank Norris, is working as an express agent for the mining company. Bagley suggests that he and Kate travel to Nevada and use Frank's inside knowledge to steal a gold shipment. When Kate reminds Bagley that Frank has gone straight, he persuades her that she will be able to change his mind. Bagley later angers the volatile Jim by reporting that Kate will not marry him and that he is also leaving town. In the ensuing brawl, Bagley inadvertantly drops Winnie's note. When Jim finds it, he also decides to head for Nevada with his men. In Bannock City, Kate approaches Winnie and offers to divert Frank from the straight and narrow. Winnie then hires her as a singer in her saloon, and as "Kate Sampson," she contrives to meet Frank. After several evenings out, Kate still has not told Frank of their plans, but when he spins his dream of starting a farm with his earnings, she pumps him for information about gold shipments. He then reveals his love for her, sending a confused Kate running back to Winnie's, where she finds Jim waiting. When Frank, who has followed Kate, arrives, Jim announces his intention of marrying Kate after they rob the gold train, and the two brothers fight. Soon after Frank defeats Jim, the stage arrives with the news that they have been robbed by Jim Plummer's gang. Privately, Frank meets with Casey Brown, the head of railroad security, who knows his real identity. Frank offers to quit his job, but Casey believes that Frank might be able to help them foil Jim's gang. At a hideout, Winnie, Kate and Jim plot the robbery. Although the gold is carried in an impregnable vault, Jim is convinced that Frank can be forced to reveal the combination. The gang is soon joined by Frank, who refuses to join their plot and warns his brother that he is loyal to the mining company. He then offers Jim his entire savings if he will take Kate and start a new life in California. Jim agrees, but as soon as he leaves, he gives the money to one of his men and orders him to purchase blasting powder. Later, Frank realizes that his effort to buy off his brother has failed. When Winnie learns that the railway is shipping a million dollars worth of gold, Kate wants to warn Frank of his danger, but Winnie locks her in her room. Later, Frank, whose real identity has been discovered by railroad official Mort Pemberton, takes the place of the assigned guard on the train. Kate manages to escape from her room and tries to alert Frank, who, telling her that their relationship is finished, refuses to listen. After the train starts to move, Pemberton tries to arrest Frank, but Kate pulls a gun on him, and he jumps from the train. While Pemberton attempts to stop the train, Frank tries to overcome Jim's gang, but is wounded by Bagley. After ordering the passengers off the train, the gang diverts it to an abandoned spurthat leads to an old mine. Realizing that Kate has sided with Frank, Jim orders her to be bound. Then he sets off an explosion which causes a small avalanche, partially burying the train. Frank releases Kate from her bonds and together they drive the train out of the shaft. When they see the steam from the train's engine, the posse heads toward the mine. Meanwhile, Jim loads Kate and the gold into a wagon and flees. Frank meets the posse and convinces him that he had nothing to do with the robbery. They then pursue the gang, forcing them to abandon Kate and the gold. During a shootout, Jim is killed. Now that Frank and Kate are exonerated, Frank plans to clear his name in Missouri and return to Nevada to marry Kate.
