A story of love and revenge, Unpardonable is the life story of Benton Steuben. Born in Washington just as the first Southern states have seceded from the Union, Steuben's life follows an alternative history for the United States in which President Lincoln chooses not to engage the Confederacy in a war. Through Steuben's personal life in Washington, professional life as a Pinkerton, and his ultimate quest for revenge; Unpardonable introduces famous and minor historical persons within their "adjusted" places in this alternative history. Steuben's own journey puts him into direct contact--and some conflict--with a number of these characters. Kept secret for many years, Steuben finally discloses his whole story as an old man to a family he meets by the Old Soldiers' home in Washington.