A plague is coming to London. Dreaded more than the Devil himself, cholera-the 'blue death'-spares no one. As fear grows across the city, Jem Flockhart and Will Quartermain are called to the bedside of a dead man, murdered, and with his throat torn out, in the back room of a brothel. When an innocent man is taken to Newgate, Jem and Will have until execution day to save him. The search for the identity of the corpse, and the killer, takes them to the gates of Blackwater Hall, home to the secretive, and corrupt Mortmain family. With the approach of autumn, no one is safe, for the fog brings with it an evil and poisonous sickness-the perfect shroud for murder.
When family secrets are prized out into the open, people begin dying. But who, or what, is the cause? Searching for answers, Jem and Will are driven underground, to the passages and tunnels beneath the city's teeming streets. Here, their adversary proves to be more elusive, and more deadly, than ever.
