Clockwork Prince by Cassandra Clare
December 6, 2011 from Margaret K. McElderry Books
The hunt is still on for Mortmain, the man who is organizing an army of clockwork monsters to destroy all Shadowhunters, and the stakes are heating up. After the break in and loss of a Pysix, the control over the Institute hangs in the balance. The Council has ordered Charlotte and the young Shadowhunters, Will and Jem, to hunt down the dangerous man and end the terror before more lives are lost. Tessa joins the hunt even though she is not a Shadowhunter. In fact, she isn't exactly sure what she is. Not a mundane. Not a warlock. Nephilim, maybe? Finding Mortmain isn't easy, he is always one step ahead of the Shadowhunters and knows their every move. How is this possible?