In the cobbled streets outside Newgate Prison, the common and desperate of London gather regularly to enjoy the spectacle of human necks broken at the end of a hangman's rope. For Rider Sandman, newly returned from the Napoleonic Wars, it is not grim entertainment that draws him here, but a mission to prove the guilt or innocence of a condemned prisoner — a duty that leads Sandman from the hellish bowels of Newgate to the scented drawing rooms of the ruthless and powerful, and into the darkest shadows of the filthy, bustling city, in search of the truth.