In an alternate Victorian London, a mechanical god named Mama Engine and her consort, Grandfather Clock descended on Whitechapel and closed the area off from the rest of the city-not to mention the world-with an impenetrable wall. No one gets out and no one gets in. Mechanical Boiler Men patrol the city and destroy those who oppose the new gods, and a disease called "clacks" turns people into clockwork men from the inside out. Some time back, the people gathered around Oliver Sumner, a former thief, and rebelled, but almost all died. Now, they're waiting for him to raise his standard again, and Oliver and the few followers he's allowed to stay with him have found a weapons that may let them destroy the gods.
This is very much a Your Mileage May Vary book. It has an awesome steampunk setting, an imaginative plot and setup, interesting characters, great fights, and great atmosphere. It's also very light on the characterization, and doesn't have a lot of plot. Take your normal fantasy novel, look at the part where you meet the hero, see the circumstances that lead to his taking action, his journey to becoming a hero, his gathering his friends, etc...and then remove everything before the part where they finally find a way to defeat the villain and go off to do so in the last 50 or so pages, except expand that to 374 pages, with references and the occasional exposition to fill you in on the rest. The entire thing takes place over only two days, and from multiple POVs, and there are a number of deus ex machinas.
If you go in expecting something deep and plot heavy, you'll probably be disappointed. Actually, remove the "probably." If you go in expecting steampunk, action, and interesting setting and don't mind if your memorable characters are on the underdeveloped side, you'll probably have a blast. Me? I went in expecting brain candy and a few thrills, so I was giddy all over the place, pretty much.
Our hero, Oliver, is a thief turned failed rebel hero. Our heroine is a former prostitute who said "screw you" to her madam and hoofed it while the hoofing was good. She also hears voices in her head. (More on that in a moment.) Mama Engine is in love with Oliver, and John Scared, one of our villains, is in love with Mama Engine. Can you say "seriously messed up conflict"? At one point, Our Hero gives Our Heroine a book, and tells her she knows he'll come back because he hasn't read the book yet, but he hears it's good. She responds properly to this bit of male stupidity. When Our Hero comes back, he takes this book off to a corner, only to be lectured by Our Heroine for his antisocial behavior, especially since there are plenty of comfy reading chairs. When Our Hero wants Our Heroine to grab the old men and run, this is the resulting conversation:
"Oh, so I'm to run off and leave the killing and the dying to the men, is that it?"
"For the love of God, woman, not now! I need shooters, Missy. No amount of smiles or sashaying will help us right now."
"You ungrateful swine!"
"This is not up for debate. Move your feet or we'll have words."
"I quite think we're having words now."
As we soon learn, assumptions should not be made regarding whether or not a woman can shoot. (And Missy is everyone's nickname for Michelle and what she prefers to go by, just for clarification.) Oliver spends a lot of time drowning in guilt over getting his rebellion killed. Michelle spends a lot of time not putting up with it much, despite having a lot more problems herself.
But basically, if you have a high octane action/fantasy/sf/steampunk-with-a-side-of-romance kink, this book probably caters to it.
Interestingly, Michelle is probably the most developed character of the lot, certainly the one that gets the most attention, but as that's spoilery and a potential hot button for some on the f-list (it usually is for me, too, but isn't here) I'll put it behind a cut.
This is also the book with the Extremely Awesome Cover that I liked enough to make an icon of it before I even read the thing. (and i'm glad I liked it, because now I can keep the icon)

And since I did like it, the icon now comes in three flavors, in case anyone besides me is actually interested:

*If I "lalala" a bit, I can tell myself that the third one is an AU Jonothon Starsmore/Chamber/Decibel.)