If I could give more than 5 stars.... I would! 
 This book was amazing! 
 Jace has gone missing since the last fight with Lilith and Sebastian is missing too. 
 So while everyone is searching for Sebastian, Clary and her friends are in search for Jace. 
 However she doesn't have to search far since Jace appears one night at her home and ask her to follow him and Sebastian. 
 The only problem is that Jace doesn't really seem like Jace at all! He does look exactly the same and behaves the same, but something is wrong about him. 
 So Clary comes up with a plan to follow them and letting her friends know all about their plans when she figoures them out, all while trying to save Jace and break his strange bond with Sebastian. 
 So even tho we know by now that Sebastian is a terrible monster who doesn't feel compasion and doesn't regret any of his actions, I couldn't help but love him. 
 Valentine truly created a monster. He treated him as such with whipping him with a demon whip so that he will never heal and be in constant pain (something he didn't put Jace through). 
 And whilst everyone thinks of Jocelyn as an incredible mother, the truth is that she is a terrible one! Not as bad as Valentine but not a better one either! 
 She constantly let him know that she should have killed him and how he doesn't matter at all to her since he is a monster and not her child, while forbidding him to come in contact with "her daughter" (which she isn't wrong about but still...) and trying to protect her. 
 In this book we see that he is lonely and will do anything to have people he thinks are like him, as companions. 
 He thinks that Jace must be like him since they were brought up by the same person so he must know how he felt. When he realized that that wasn't the case he tried to connect with Clary since they're sibblings so the must be alike... 
 Even tho everyone in this series think that he is incapable of love, I do belive that he loves Clary but can't comprehend that feeling so he confuses it with lust and something else. 
 The truth however is that the only monsters in this story are Valentine and Jocelyn. 
 Jocelyn gave up on him even when he was a little baby, even before she thought that he was dead. 
 And Valentine.... well Valentine did everything else! 
 He made him a demon, he told him that no one in this world would ever love him because he is a monster, he abused him in every possible way he could and at last never was proud of him (the only thing Jonathan ever really wanted) and felt all his fatherly toward Jace instead of his actual son.