Irene must be top of her game or she'll be off the case. Permanently ... Irene is a dimension-hopping 'book spy' for the secretive Library. And along with her enigmatic assistant Kai, they're posted to an alternative London to retrieve a dangerous book. But some will kill to retain it.

Stealing a book is standard, if required, but nothing has prepared them for the dangers in store. This world is chaos-infested, so the usual laws of nature have been bent to allow werewolves, fae and unpredictable magic. Irene's new assistant is hiding a few secrets of his own. And when they arrive, the book they seek has already been lifted - by a notorious lady cat-burglar. Plus London's underground factions seem prepared to fight to the death to get 'her book'.

Soon, she's up to her eyebrows in thieves, murderers, secret societies, the fae and giant mechanical centipedes. Good thing Irene can call on the aid of a deer-stalker wearing detective (who bears more than a passing similarity to a certain fictional sleuth) for assistance.

And when things get tough, Irene is more than ready to do whatever it takes. For this assignment could endanger The Library and the nature of reality itself.