I had to think long and hard before writing my review for City of Lost Souls and giving it a rating. I ended up giving it five stars, not because it's the best book ever, but because it had me doubting myself.It's not very often that I come across a book that has me questioning what I believed of a person. Bad is bad, right? Wrong. In this installment of The Mortal Instruments, Cassandra has me thinking that maybe the bad guy isn't all bad. I see a side of Sebastian that has me dumbfounded and shaken, but a good kind of shaken. Too often I have read books where the bad guy remains the same, but not this one. It leaves me wanting to know more.I think it's Cassandra's characters that keep me coming back for more, more than the actual plot itself. It's the complexities that I enjoy. I think Cassandra enjoys torturing her characters and, in this case, I think it's to her credit.Take the following:Jace and Clary are totally in love with each other, but have never had it easy - not from the first book. In this installment, imagine seeing the boy you love fawn over a boy you despise - even if he is your brother. Or Magnus and Alec - just when you think everything in their relationship is running smoothly, bam, Cassandra adds an element that may lead to disaster. (not saying what because that would be a spoiler)Clary and Jocelyn - Yes, the mother and daughter who once had a close relationship continues to crumble.Then there's Simon, Luke, Jordan, Maia and the list goes on. Yes, there are a lot of characters, but it works. I've been hooked since the first book, mainly because Cassandra has a way of bringing her characters alive for me. I am definitely looking forward to the next and maybe last installment, but not because of Jace and Clary. It's because of Sebastian. Up to now, I had always just wanted to read more about Jace, Clary and Simon.I find that rather strange when I think about it.