A young Confederate captain with a grisly past as a cavalry raider in Tennessee is on his way home to his family plantation north of Houston in the last days of the Civil War. In Austin, Capt. Jerod Robin is accused of murder and is thrown into the stockade by U.S. Army Capt. Santana Leatherwood, a Texan whose family has feuded bitterly for decades with the Robin family. In the stockade Robin meets British novelist and adventurer Edmund Varney, in Austin to write the life story of Lt. Tom Custer, heroic younger brother of famous General George Armstrong Custer. Varney is charged with attempting to steal Tom Custer's legendary warhorse, Athena, upon whose back Custer recently won two Congressional Medals of Honor. The two prisoners stand trial beside a 16-year-old mulatto girl, Flora Bowprie, who has come from New Orleans searching for her father but has been arrested as a runaway slave. Homicidal events cause the rebel captain, the British author and the young fortuneteller to flee from a Cavalry squad led by Santana Leatherwood and Tom Custer, mounted on his great Arabian horse. The story races to the inevitable showdown between the Robins and Leatherwoods, two families on opposite sides in the Civil War. But, before the final confrontation Jerod Robin hears a dark accusation about his birth and his mother that lends a special ferocity to the showdown. Then the story of "Custer's Brother's Horse" takes a surprising twist. This is a horse for the ages.