This book felt more like a novella than an actual novel. 
 Simon was the protagonist through out most of the book 
 I Hate Simon. He's even more annoying than Clary (which says alot), and his mark of Cain. 
 This however didn't make the book less entertaining. 
 The other main focus was Jace and Clary's relationship and the nightmares that Jace has that make him keep his distance from Clary. 
 Sidenote: 
 Reading this book after reading The Infernal Devices was a bad idea since everytime Camille, WIll or (view spoiler)[Jem (hide spoiler)] were mentioned... I got so excited that I didn't pay any attention to what happend.