A Darker Shade of Magic

I confess that this books cool cover was the first thing that drew me in. Then seeing that it was highly rated among thousands of Amazon users... And then finding out that the sequel was also highly rated... And of course the cool premise. Namely that there are four Londons that our protagonist, Kell, can navigate between. These Londons are all capitals of different countries with different monarchs. Grey London has very little magic and is ruled by George III. Red London (which Kell calls home) is the seat of the Maresh empire and is flush with magic. White London is ruled by the psychotic Dane siblings, Athos and Astrid, and is losing magic fast. And Black London, which no one talks about and has been largely cut off since magic went wild there. Trouble starts when Kell comes into possession of a dangerous magical artefact from Black London. Story moves briskly and I has to read the final hundred pages all at once.