Unpardonable follows an alternative history from 1861 through 1938 as seen through the life of a fictional character, Benton Steuben. Steuben serves as the narrator of his life story as an old man speaking to a young family during the winter of 1937–38 with each chapter of the story being introduced chronologically by a newspaper headline from a particular day in history.
A Pinkerton detective, Steuben's story is one of revenge against his young wife's kidnappers and murderers. The multi-decade search takes Steuben through the United States and the Confederacy of the late 1800s and early 1900s, where he runs into local characters, minor characters in history, and also some prominent historical figures.
Whenever possible, names, dates, and places reflect actual history or history that would have potentially occurred in this alternative history without the Civil War. All but the main characters in the book actually existed at the addresses and dates specified in the story.
Of course, the alternative history changes some lifespans and careers. For example, Virginians Jeb Stuart and John Mosby occupy significant positions in this U.S. government, while Ulysses Grant makes no appearance in the newspapers of the time. Similarly, James Blaine and Judah Benjamin become U.S. Presidents, while U.S. Grant, Benjamin Harrison, Rutherford Hayes, Chester Arthur, and Woodrow Wilson never do.
Certain events known to history either occur at different times or do not occur at all. In addition to the Civil War, Reconstruction and (U.S.) Prohibition never occur. These removals allow resources to be deployed elsewhere and cause, for example, early completions of the Transcontinental Railroad and the Washington Monument. Germany's failed attempt to divert the United States into a war with Mexico during World War I becomes partially successful in this alternative history where the Confederacy must spend those years fighting a (losing) war with Mexico.
The Peckertski family to whom Benton tells his story lived as they did in the book. The author's late father, Benton, was born in February 1938 in Washington, DC. His father's family changed their name from Peckertski to Becker several decades earlier at Ellis Island