A band of vigilante executioners roam the hot summer nights, abducting evil men who they judge unworthy of living and hanging them by the neck until dead. But do these rogue hangmen crave true justice --- or just blood? As the bodies pile up and violence explodes all over the sweltering city, DC Max Wolfe embarks on his most dangerous investigation yet, hunting a righteous gang of vigilante killers who many believe to be heroes. But before The Hanging Club is confronted, Max must learn some painful truths about the fragile line between good and evil, innocence and guilt, justice and retribution.

On New Year's Day, a wealthy family is found slaughtered inside their exclusive gated community, their youngest child stolen away. The murder weapon leads homicide detective Max Wolfe to a dusty corner of Scotland Yard's Black Museum devoted to a mass murderer who, 30 years ago, was known as The Slaughter Man. But The Slaughter Man has done his time and is now old and dying. Is he really back in the killing game? And was the slaughter of a happy family a mindless killing spree, or a grotesque homage by a copycat killer, or a contract hit designed to frame a dying man?

Someone has been violently killing members of London society. The killer is strong enough and smart enough to kill with a single knife stroke, and bold enough to kill in public. When Detective Max Wolfe realizes that the victims may have all crossed paths decades ago at their exclusive private school, the case changes. Suddenly, the murders look less random and more personal, and Max finds the killer's reach getting closer to everything --- and everyone --- he loves.