On 6 May 1842, an unknown assailant shot Lilburn Boggs, former governor of Missouri and author of the infamous extermination order against the Mormons. Though given up for dead and widely reported killed, Boggs survived. The crime was never solved. Twenty-five years after the fact, seeking closure if not justice, his family hired a Pinkerton agent to examine the evidence and identify the assailant. From the West Coast to the banks of the Mississippi, from the Missouri River to the shores of the Great Salt lake, the detective follows a trail that leads, inevitably, to the notorious Mormon gunfighter Porter Rockwell.