When ambitious apprentice chemist and secret alchemist Peter Woulfe is tasked with caring for a mysterious illustrated book, the Mutus Liber, he quickly realises that the grimy underworld of Georgian London is even more dangerous than he first believed.

Soon the book is stolen by the light-fingered Sukie and Peter finds himself being pursued by threatening men who are willing to do anything to get the book back. Where in teeming London might Sukie be found? Why is Peter so enthralled by her? And what is it about the Mutus Liber that is so enticing? As the search for the book becomes an urgent game of cat and mouse, it seems that the key to Peter's present dilemma might only be found in half-remembered events from his childhood, and then further back still, in the mists of Irish myth.