John "Kit" McKittredge is a young Union officer from Maine who is terribly wounded in one of the first battles of the Civil War. Still unfit for active duty after nine months in the hospital, he is recruited by an unorthodox colonel named Valentine Burdette to work in the Provost Marshal General's Department in Washington.

The beleaguered capital, now swollen to seven times its prewar population, is filled with saloons, brothels, spies, thieves, and murderers. It is also rife with official corruption and political intrigue.

While investigating what appears to be a routine case of military procurement fraud, Kit becomes embroiled in the murder of a beautiful young woman who has had the misfortune to attend the birthday party of Union General Joseph Hooker, the notorious and charming libertine.

The investigation leads Kit through a series of harrowing adventures - both on the battlefield and in the capital's darkest dens of depravity -until he and Val Burdette must confront a vast criminal conspiracy that threatens both their own lives as well as the fate of the Republic.