What exactly is this book? Well, it's sort of a Victorian era historical romance, but steampunky. Oh, and it's sort of an urban fantasy, full of vampires, werewolves with ghosts in the background. It's also clearly a great opportunity for the author to show off some fantastically detailed knowledge -- the description of the meal at the wedding at the ending is very impressive. I had some problems with what I suspect were editing lapses ("mollified her tone", "catch of the first water"). Technically, they aren't wrong -- they just don't sound right, either. For example, "of the first water" is right for the time, as, of course, is catch. But putting "catch" and "water" together like that makes the mixed metaphor extremely jarring. Perhaps one can mollify one's tone, but generally one would moderate one's tone to mollify a person.
http://en.wiktionary.org/wiki/mollify, see the usage from _Rinkitink in Oz_ -- the goat was mollified by the respectful tone used.
So enough with the niggling. This thing was a blast! I loved it! I've pre-ordered the second in the series, because just because Carriger married off her heroine doesn't mean she's done with her. Yay! I do love interconnected romance series in which the main pair from one are in the background of others (and vice versa), but I also love it when marriage isn't treated as The End.
Our heroine is the "soulless" preternatural of the title. Her kind is rare, but breeds true: her father was the same. He died sometime in the past and Alexia now lives with her mother, stepfather, two silly stepsisters, in London. Because Alexia's father was Italian, Alexia isn't the kind of pale blonde popular at the time; her mother doesn't even bother with a Season for her. Now, at 26, she's become almost uncontrollable in her wanderings about at all hours of the day and night with various Characters. She'd like to get a job with the bureau that keeps an eye on (and out for) the supernaturals, but while they hire preternaturals and they hire women, there's no way they're going to hire a single woman preternatural of her class. But a variety of people have an eye out for Alexia's future, and she keeps ending up in mysterious situations as a rove vampire and an alpha werewolf try to figure out where the fresh vampires are coming from (such as the one Alexia offs with a hairstick in the library at a ball at the very beginning of the book).
Historical romances suffer from a really substantial problem: young single women (the kind that a reader today is assumed to want to read about) in the past generally didn't have much freedom, power, or resources. The exceptions ("Originals", bluestockings, women raised by fathers with no sons who decided to just treat one of the daughters as if she were a son, widows, marriages of convenience, or being so wealthy/having so perfect an ancestry that no one can really get away with completely cutting you out of society) are ruthlessly exploited. Carriger appears to have decided to adopt a sort of Amelia Peabody use-several strategy. It works reasonably well. I particularly like, however, that Alexia barely notices that she keeps getting invited to parties -- largely because she's such an entertaining conversationalist.
Definitely worth a few hours of your time.