In the late 1880's, the development of the Canadian Pacific Railroad is halted by the enormous challenge of finding a route through the Rocky Mountains. At a meeting of the Canadian Parliament, Canadian Pacific general manager William Van Horne reports that surveyor Tom Andrews is in the field attempting to map a route through the mountains. While doing his work, however, Tom is shot at by a fur trader, Dirk Rourke, and his accomplice Cagle. When Tom returns to the railroad construction camp to report to Van Horne, he spots Cagle working there and attacks him. However, Dr. Edith Cabot intervenes and makes Tom aware of her pacifist philosphy, which does not impress him. After he delivers his proposal to Van Horne, Tom heads for Calgary, where his girl friend, Cecille Gautier, is waiting for him on her family's ranch. Rourke has been attempting to court Cecille but she has rejected him. Tom and Cecille's father attend a meeting at Rourke's trading post, where Rourke campaigns against the railroad, saying that it will mean the end of trade in the area. When Tom tries to convince the trappers and farmers that the railroad will bring them many benefits and that Rourke is against it because it will end his business monopoly, he and Rourke become involved in a fistfight, which is broken up by Père Lacombe, whom Cecille has sent. Tom decides to return to the railroad to help to keep peace, prompting Cecille to break their engagement. At the camp, explosives expert Dynamite Dawson tells Tom he suspects Indians of stealing dynamite, and Tom later finds several cases of dynamite buried at an Indian village. The chief apologizes to Tom, saying that some young braves have been paid by a white man to steal the explosives. As Tom unloads the cases back at the camp, Cagle and Rourke shoot at one, causing a large explosion that seriously injures Tom. While on board a train back to the base hospital, Dr. Cabot transfuses her own blood and saves Tom's life. Cecille, meanwhile, overhears Rourke, her father and others plotting to stop the railroad by having the Indians cause trouble and when she objects, her father threatens to disown her. Cecille, who suspects Rourke of having caused the explosion which injured Tom, plans to join Tom at the hospital, but Dynamite persuades her to return home to gather more evidence to pass onto him. A series of explosions, the work of saboteurs, closes down construction on the railroad for the winter. By the spring, Tom has almost fully recovered, and he and Edith are in love. Hearing that there is trouble at the work camp, Tom prepares to return, but Edith persuades him not to wear a gun. Rourke has been stirring up the Indians and has established a saloon and gambling hall at the camp. When a man is shot at the saloon, Edith goes to help but is too late. Tom straps on his guns again and closes down the saloon. Cecille then arrives with the news that Rourke and the Indians are about to attack, and Dynamite rides off to get reinforcements while Tom and the others take refuge in the hospital car. After Cecille's injured father is brought in and tells them that they are considerably outnumbered, Tom goes after Rourke and Cagle and, as the Indians prepare for a final attack, shoots Cagle. Rourke is then killed by a falling tree that had been set on fire as a signal to the Indians. Finally, Van Horne and reinforcements arrive, and the Indians are driven off. Later, however, the Indians walk into the camp and say they want peace. Dismayed by all the violence she has witnessed, Edith heads back East, leaving Tom and Cecille together.