This is a likable book that starts off a little bland but gathers momentum pretty quickly to become, ultimately, a lot of fun.
As a person who has read a good bit of historical fiction set in this time period (Regency England), it makes me laugh when an author's research clearly consists of reading some other author's historical romance, and her (it's usually a her, Mr. Nix being a rather unexpected and cool exception) research consisted of reading a third author's historical romance (Georgette Heyer is pretty much guaranteed to get into the chain somewhere) and thus we always see the name Lady Jersey and learn that her ironic nickname is "Silence," or we hear about some neck-or-nothing young blood of the fancy getting in his cups and acting like a slow-top. Nix, however, broke out some vocabulary that even I, the avid consumer of recycled quaint phraseology that I am, hadn't heard before. (Cock-a-hoop, anyone? It's not dirty, I promise.) He definitely didn't just pick that up from an Amanda Quick novel. (It's not period specific, but I actually had to use a dictionary for another word that appeared in this book -- inimical. I assume some [many? you, my friends, are generally a literate lot...] of you know it and wonder how I managed not to, but there you are. I did miss a couple of points on my verbal SAT. Nobody['s vocabulary]'s perfect.)
Anyway, back toward the vicinity of topic! Virtually every component of this plot is a common trope: girl is in disguise as a guy... said girl meets the guy she crushes on while in said disguise [which, I must point out, includes an ensorcelled mustache that cracks me the heck up]... said guy has Secrets... said guy might or might not be betrothed already to another girl who inserts herself in the heroine's life to 'ask' her to back off her man, heroine holds back tears and pretends not to care. Misunderstandings! Near disaster! True love prevails! Whew! And there's basically a fairy godmother in the form of a [just slightly overwritten] hilariously brash great-aunt who says all the rude and witty things you wish you could get away with, while the villainess is a bitter, crazy, dark vixen. But Nix has managed to combine them in a way that feels playful and engaging, if not exactly revelatory.
And there are some unique details. I've definitely never read about two people getting tied up together in a booze barrel and getting drunk from the fumes and laughing uncontrollably even while contriving to get out of the barrel so as not to be drowned at sea. That was a fun scene. And Truthful did some pretty clever stuff like crafting a makeshift anchor to slow the ship down so that her rescuers' boat could overtake them at sea. She also surprisingly kicked some ass in a fight with a traitor who punched her in the face. But then she came back home and was heartbroken and mopey and didn't stay inside when people told her to stay inside (to avoid being captured by the psychotic killer who wanted to use her to destroy the world), and we ventured back into generic tropeville for a while before the happy ending.
Just a matter of personal taste, I never really came around to liking the heroine's name: Truthful. Clearly it doesn't ruin the book or anything dire, but the whole way through I always found it a little jarring. And I didn't find it all that rewardingly precious when people called her Newt, either. (Really, the only naming thing I liked for her was the one time her sweetheart called her Tru. But then later he called her Newt, too, and I was like Dude, you are such a slow-top.) What poor sort of person has a nickname because she has a pretty bad name, but the nickname is arguably even worse? I wished I could have read this in an e-reader and found & replaced Truthful with something more charmingly unique but not outright odd. Portia or Rosalind, maybe -- a little tribute to Shakespeare's cross dressing super chicks would have been a nice choice, perhaps.
Ultimately, though, I wholeheartedly recommend this novel if you read frequently from its genre(s) and really like the feeling of familiarity when you return to 1800s London and spend time with fashionable young ladies who are falling in love and having fairly unbelievable adventures, given that they are gently-bred young ladies in early 1800s London and normally wouldn't be able to do anything that involves men, pants, sweat, or fun. If you've been living in cryogenic stasis or an underground bunker for untold decades and never encountered a book of this stripe, I'd still say yeah, go ahead and read it because it's a nice, wholesome, clever diverting book with magic and an impressive vocabulary that won't shock and horrify you like the stuff on the Internet and that miserable, wretched Game of Thrones series everyone's talking about.