This is a sequel to A Spy Wears Two Hats, the young adult historical fiction novel pertaining to the Civil War that had ended recently. The hero, Tommy Miller, had been recruited by Captain John Mosby in 1862 to go undercover for The Confederacy and report to General Lee's Command on Yankee movements. That novel climaxed with the Battle of Antietam. This work climaxes with The Battle At The Little Big Horn River. In this adventure story, Tommy now 29, moves forward with his detective bureau, which he started with partner Roger Pinkerton after President Lincoln's assassination. The detective agency is tracking George Armstrong Custer per Mosby's direction from Washington D. C. Custer's missteps in dealing with the frontier Indian problem result in his own slaughter, that Tommy witnesses on horseback atop a nearby butte, in the Montana Territory on the banks of The Little Big Horn River.