If you have been reading the negative reviews about this book here on goodreads and have decided not to read it, thinking it just a Victorian rehash of City of Bones, DON'T LISTEN TO THESE NUTCASES WHO OBVIOUSLY HAVE NO IDEA WHAT CHARACTER TRAITS ARE COMPARABLE/SIMILAR AND WHICH ARE NOT! 
 I can't tell you how many people whined that Tessa, Jem, and Will were identical to Clary, Simeon, and Jace (oh and that Isabelle and Jessamine were exactly alike). And after reading this book all I can think of is "What books did THEY read?" 
 Tessa could not BE more different from Clary. Clary is an artist and anything from her POV tends to get very purple prose-ish, whereas Tessa is a bookworm whose worst crime is comparing everything to novels I personally can't stand (Tale of two cities/Pride and Prejudice...yuck...though I do agree with her on the Wuthering Heights front; that book's freaking AWESOME). Jace and Will have nothing in common save that they are both sarcastic trolls who use wit to cover up deeper personal issues. And Simeon and Jem? I can't think of a single trait they have in common. I actually liked Simeon a lot in City of Bones, but Jem bored me to distraction and I think is part of the reason it took me so long to finish this book. As for Jessamine, she is a GREAT character, quite similar to Sansa Stark from Game of Thrones, but nothing whatsoever like Isabelle. 
 That out of the way, onto the plot! 
 Basically it centers around Warlock (sort of) Tessa as she discovers Downworld and Shadowworld after getting kidnapped and then rescued by the witty Will Herondale. There isn't much story for the first chunk of the book, just Tessa getting ill-treated and making discoveries and friends/allies, but the pacing is so good you won't notice the plot hasn't yet arrived. The plot arrives in the form of Tessa shapeshifting into a vampire and going undercover to discover who the villain is. I won't spoil it here, but it's a MAJOR red herring, expertly pulled off. 
 As cliche as it might sound, it really is a brilliant book, right up until...sigh... The End... Basically, the end was a suckish cliffhanger. I know it's a series, but jeeze, nothing's really resolved and for those of us who don't have a copy of "Clockwork Prince" immediately at a hand, it's pretty irritating. 
 But by all means, YES, read this book! It's every bit as good as City of Bones (if not better) and different enough from it to hold your attention.