The episode follows the construction of the Pacific Railroad, the first transcontinental rail system, which would unite the eastern and western seaboards of the United States. Started in Sacramento by a consortium of local shopkeepers with no experience in building a railroad, the episode follows their efforts to build from west to east through the forbidding Sierra Nevada mountains with the help of Chinese labourers whilst simultaneously following the efforts of the workers of the Union Pacific to build from east to west, and their problems in dealing with the lawless nature of the wild west, attacks by Native American raiding parties, and financial corruption and scandal.