There are four parallel Earths in this book, each just a quick dimension apart. Each has a city called London in the same place on the Thames, but they have different languages, different countries, different histories. The biggest difference, however, is the level and role of magic in each city.
- Grey London has almost no magic - and matches our London under Mad King George.
- Red London is rich in magic, and people live in harmony with the magic.
- White London is poor in magic, and people strive to steal, control, and dominate the magic as much as they can.
- Black London is dead: here, people had let themselves be controlled by their magic, and the world had experienced a mysterious apocalypse as a result.
There are only two magicians left who can travel between worlds: Kell, from Red London, and Holland, from White London. They act as messengers between the royal families of the three Londons that are still accessible. Black London has been sealed off to prevent its apocalypse from spreading into the other dimensions.
Kell is our hero, and the story really kicks off when he smuggles an artefact (which is treason) that turns out to be a relic from Black London (which makes it powerful and dangerous). Suddenly, all kinds of nefarious characters and thugs are after Kell. To make things worse, he gets entangled with Lila, a tough teenaged orphan girl from Grey London who wants nothing more than to be a pirate captain and see the world...
A Darker Shade of Magic has all the right ingredients: a good pace, repartee between the good guys, sinister and creepy baddies, adventure and magic... it's great fun to read.
It's not flawless: there are some holes in the plot, and while it is nominally set in (four) London(s), Grey London doesn't quite feel like UK London to me. In terms of plotholes, it's never quite clear what the royal families in the different Londons have to say to each other / why any connection continues to exist, and what magic can and can't do is quite nebulous. It feels a little as if the author hasn't quite worked out the workings of magic in her worlds. Still, these are flaws only some (overly pernickety) readers will mind: I think most readers who like to read the occasional fantasy novel will thoroughly enjoy A Darker Shade of Magic. I certainly did.