During the waning days of the fur trade, greenhorn Jim Baker joins legendary frontiersman Jim Bridger on an expedition to the far west. The young, red-headed adventurer falls in love with the frontier and the free lifestyle of a trapper, and he quickly develops a reputation as a skilled marksman and mountain man. But trouble is brewing in the mountains and the prairies. Incensed by the encroachment of white pioneers, the Sioux, Arapaho, and Cheyenne begin to wage war against trappers and their Shoshone allies. When Bridger learns that his partner Henry Fraeb might be in danger, he sends Baker to find him. Unable to retreat, Fraeb and Baker build a rudimentary fortification and prepare to defend the small party of trappers against hundreds of warriors. Before the battle is over, Baker is thrust into a leadership role that will determine the fate of the men.