Transported through time to the dank streets of Victorian London, Alex Locke seeks to unravel the mysteries of the Obsidian Heart, the enigmatic object to which his fate is inextricably bound. When a string of grisly murders takes place across the capital, Alex follows a trail that will lead him through the opium dens of Limehouse into the dark and twisted world of the Society of Blood, and ever closer to unlocking the secret of the Heart.