John Whyte, the estranged, youngest brother of the Duke of Bransworth, and late Colonel of the First Brigade, Michigan Volunteer Cavalry during the Civil War, is at loose ends. The war has ended and he has tragically lost his fiancée to a needless attack by a wayward confederate soldier. He decides to visit to his friend, General Phil Sheridan, in Chicago, where the Civil War hero has been assigned as Commander of the Western Territories.
Sheridan suggests that John look at opportunities with the newly organized Pinkerton Detective agency founded by Allen Pinkerton, a man John had worked with early In the war at the request of President Lincoln. John agrees and listens to Pinkerton's offer of a position in St Louis as a special agent for the detective agency, accepting only the most demanding and interesting cases, so John may also develop a home in the area.