Josiah Wakefield and Dan Sturgis are young civil war veterans, employed in the Territory of Nebraska by the Union Pacific Railroad to hunt down the hired gunmen who are wrecking their supply trains. As robbery is clearly not the motive, someone must be trying to slow up the railroad's westward progress. After a vicious firefight on the trackless plains, their continued pursuit takes them to the dissolute city of Omaha where, in the company of their new acquaintance, Bill Hickok, they survive an ambush by some paid assassins. Their trouble is only just beginning, and they are to face deadly city marshal, Deke Pritchett, and the perils of being on board an Iron Horse, before a momentous finale. But just whose side is Bill Hickok really on?