Steampunk action and adventure in a -- well, not alternate world. You can recognize the influences -- large parts of it are nineteeth-century -- but it's parallel elements in an imaginary world, not strictly speaking a parallel world.
And a lovely imaginary world it is. A Parliamentary-ruled Jackals, where the equivalent of the English Civil War ended up much worse for the royalist side. They had a king, who is much worse off than a mere figurehead. Quartershift, where the French Revolution went on a little long. And you have the Circlist church and the Carlist rabble-rousers and the world-singers and the feymist touching the feybreed, of whom the lucky ones get to form the Special Guard. And the steam men, under the rule of King Steam, whose talk is one of the great charms of the book. . . . I love this world. Revealed in great and convincing detail in lovely language.
My only complaint was that one magical thing was not even hinted at where it came from. True there were shadowy origins for a number of things, but convincing ones, and this one could have had a little more. But that was only one detail.
And set loose in this world we have Molly, an orphan in a workhouse, and Oliver, an orphan boy touched by the feymist but manifesting no signs of it, leading to his being "registered" and forbidden to leave his uncle's house. Except that violence and murder precipitate them out into the world for a plot I don't even think I am going to try to explain even the beginning of. The stakes got a little high for my taste, but without the great danger of too high stakes, making the world look flimsy. And at one point I remember thinking that Molly seemed an especially special snowflake -- but All Was Explained, and not long after, either.