City of Lost Souls by Cassandra Clare

If you have not read the first book in this series you need to. The first book is City of Bones.These books have to be read in order.
     Thankfully, Clare got back on the trail and out of the woods. This book was much better than the last, City of Fallen Angels.     In the last book Luke and Jocelyn were preparing for their wedding, and the wolf pack was having a party in their honor. Clary and Jace were having relationship trouble, Jace was keeping some things that were happening to him secret, and he thought he was a danger to Clary.      Simon was seeing Izzy and Maia and neither knew he was seeing the other, in the end the truth came out. Simon gets a new roommate, Jordan, who turns out not only to be of The Praetor member, a group of werewolves who help other new downworlders deal with what they are and get them on the straight path. He also happens to be the Jordan who bit Maia, and eventually these two cross paths and begin to deal with what had happened.
     Alec and Magnus are traveling around the world. Maryse and her husband are separated.  It turns out, that Max was the only reason keeping them together. Simon slips and attacks Maureen, Jordan stops him from possibly killing her.
     A baby is found with a note asking to kill it. This begins, the strange events that lead up to a major discovery. Someone has interest in Simon, first it is a music agent, and then Maureen is abducted for she is mistaken as Simon's girlfriend. She is turned into a vampire, by choice.
     Jace being risen from the dead is discovered and he needs a ceremony redone to protect him from demonic possession. It doesn't happen in time. In a dream, Jace becomes marked by the demon, Lilith. Clary, is kidnapped by Jace, and used to lure Simon to Lilith. Lilith uses Simon's blood to wake Sebastian. Because Jace was risen from the dead, one of the dark side can be raised from the dead. Sebastian is brought back and is connected to Jace by the spell Lilith used. What happens to one, happens to the other. Oh, and Simon put himself in Lilith's path, and since she was whipping Clary, she hit Simon and the Mark of Cain, destroyed her.
     In City of Lost Souls, Clare's back to the writing an interesting and captivating story. This story continues where the last left, with the aftermath of the encounter with Lilith, and the disappearance of Jace and Sebastian. How far will Jace's friends and family go to get him back? This is one of those pivotal books in a series. Of course, there is more character growth, but the biggest part of this story, is the revelation of Sebastian's plan. A taste, of what the Shadowhunters will face, and a character development, that was bit of a surprise to me, that will definitely shake things up for Downworlders and Shadowhunters a like.