A Darker Shade of Magic

Kell is one of the last travellers-magicians with a rare ability to travel between parallel universes connected by one magical city. There's Grey London, without magic and ruled by the mad King George III. Red London-where magic is revered, and where Kell was raised alongside the heir to the empire. White London-where people fight to control the remaining magic and magic fights back. And once there was Black London...