Coincidentally in the same action, a maverick known as Cassidy was killed by accident. Cassidy is the hero of the story and it is what lay behind Cassidy's relationship with Hardin that launches the narrative.
Two men set out separately to find the truth. One is McNeill a Federal ambassador and ex-Confederate General. The other is Oppenheim the owner/editor of the El Paso Times.
The journey introduces us to John Jumping Horse a full-blooded Brule Sioux, Federal agent and blood brother of Cassidy. We meet Rabbi Ben Yochai the spiritual friend of Cassidy's saintly father and we are immersed in the sordid lifestyle of a country that was only partly ready to be tamed.
We trek to the immigration port of Galveston from where Cassidy's forbears embarked on their journey and we go to Huntsville Penitentiary where Hardin spent many years of his short life before emerging as a lawyer.
The story comes together through Cassidy's diary recounting the meetings he had in the penitentiary with Hardin. We learn of the roots of Cassidy's family in Eastern Europe and we see them interact with his adopted Sioux family to produce a personality and a philosophy the like of which we will never see again.
As a result Hardin, the fastest gun in the west and one of the brightest, who never killed a man who didn't need killing, was granted an early release.