How can an elderly recluse drown in a chair in her otherwise dry basement? That’s what John May and Arthur Bryant of London’s Peculiar Crimes Unit set out to discover in a city rife with shady real estate developers, racist threats, dodgy academicians, and someone dangerously obsessed with Egyptian mythology. Linking them all is an evil lurking in London’s vast and forgotten underground river system—a killer with the eerie ability to strike anywhere, anytime, without leaving a clue. It’s a subterranean case of secrets, lies, and multiple murder that defies not only the law, but reason itself. Can Bryant and May bring a killer to the surface and stop the dark tide of murder before it pulls them under, too?