This book allows you to see how unrational side of what is the Shadowhunters. When a family is shunned from the rest of the clan, they get very drastic and will do anything to get payback or to be welcomed back again.
I know that the new series that we are going to get in a few months involves the girl with the last name Blackthorn, and we see her lineage in this book. Also, we see a lineage in the Herondale family.
I love learning more about Magnus’ past though. It explains a lot more of his personality and why he does the things that he does. He is probably the best character that Clare has wrote honestly.