From the New York Times bestselling author and legendary storyteller Alan Moore, the first book in an enthralling new series about murder, magic, and madness set between two Londons-one recovering from World War II, and one a secret world unlike any other.

"Extraordinary . . . very funny . . . It does what fantasy does best which is show us something beyond our experience." -Susanna Clarke, New York Times bestselling author of Piranesi and Jonathan Strange & Mr Norrell

In 1949, amidst the smog of London, Dennis Knuckleyard, a hapless eighteen year-old employed by a second-hand bookshop, discovers a novel that simply does not exist. It is a fictitious book, one only existing within another novel. Yet it is physically there in his hands. How?

Dennis has stumbled on a book from the Great When, a magical version of London beyond time and space, where reality blurs with fiction and concepts such as Crime and Poetry are incarnated as wondrous, terrible beings. But this other, magical London must remain a secret: if Dennis cannot find a way to return this book to where it belongs, he risks facing gruesome and grave repercussions.

So begins a journey delving deep into the city's occult underbelly and tarrying with an eccentric cast of sorcerers, gangsters, and murderers - some from legend, some frighteningly real, and all with plans of their own. Soon Dennis finds himself at the center of an explosive series of events that may alter and endanger both Londons forever . . .