Introduction: The Final Descent (The Monstrumologist #4) Will Henry and Dr. Warthrop have encountered many horrors together鈥攂ut can Will endure a monstrumological terror without his mentor? Will Henry has been through more that seems possible for a boy of fourteen. He鈥檚 been on the brink of death on more than one occasion, he has gazed into hell鈥攁nd 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 Will鈥檚 loyalties may be shifting, he turns on Will with a fury, determined to reclaim his young apprentice鈥檚 devotion. And so Will must face one of the most horrific creatures of his monstrumology career鈥攁nd he must face it alone. Over the course of one day, Will鈥檚 life鈥攁nd Pellinor Warthrop鈥檚 destiny鈥攚ill lie in balance. In the terrifying depths of the Monstrumarium, they will face a monster more terrible than any they could have imagined鈥攁nd their fates will be decided....