Rick Yancey 
Final Descent 

In the fourth and final horrific adventure in the award-winning Monstrumologist series, Will Henry encounters unprecedented terror, a terror that delves into the depths of the human soul.Will Henry has been through more than seems possible for a boy of fourteen. Hes been on the brink of death on more than one occasion, he has gazed into helland hell has stared back at him, and known his face. But through it all, Dr. Warthrop has been at his side.When Dr. Warthrop fears that Wills loyalties may be shifting, he turns on Will with a fury, determined to reclaim his young apprentices devotion. And so Will must face one of the most horrific creatures of his monstrumology careerand he must face it alone.Over the course of one day, Wills lifeand Pellinor Warthrops destinywill hang in the balance. In the terrifying depths of the Monstrumarium, they will face a monster more terrible than any they could have imaginedand their fates will be decided.Beyond a simple finale, this is a brave statement about the duplexity of good and evil, and the deadly trap in which all of us are snared (Booklist, starred review).