The Monstrumologist is author Rick Yancey's horror novel for young adults. It follows a young orphan named Will Henry in 19th century America, who is the assistant of Dr. Pellinore Warthorpe's, who is a specialist in monstrumology, or the study of monsters. Dr. Wathrope is an eccentric and strange man (hence his profession) who deals with some of the most gruesome things in the world.
Over the course of his time with Dr. Wathrope, Will chronicles his experiences in a journal, which he keeps up dutifully. Throughout his life, Dr. Wathrope treated Will with tremendous kindness and charity, something which has left Will feeling indebted to the eccentric doctor who Will likes, but finds strange. It was Dr. Wathrope, and only Dr. Wathrope, after all, that offered Will a place to live and food after his parents tragically died in a mysterious fire.
Yancey's novel is told from the perspective of an unnamed narrator who finds Will's aforementioned diaries many years after he had written them. And while Will was grateful for the shelter and food that Dr. Wathrope had provided him, the journals make it clear that his childhood was far from easy. In fact, he spent much of his childhood fearing for his life—but often because of humans, not the monsters Dr. Wathrope studied.
One day, a grave robber barges into Dr. Wathrope's home late at night and hands the good doctor a package that he claims has a monster inside it. Dr. Wathrope takes the package; the man gives him money for taking the box.
After looking inside the package, Dr. Wathrope determines that an Anthropophagi, or cannibal possessing profound strength, is inside. But the Anthropophagi is dead, having killed and partially digested a person prior to its death. Will vomits at this discovery—something which he frequently did while living with the enigmatic Dr. Wathrope.
Wathrope is perplexed because the Anthropophagi is not native to America. He must discover where the monster came from and if it had infested other parts of America. To that end, Dr. Wathrope calls Erasmus for help. The two begin to search for more Anthropophagi in graveyards; if there are more out there, they will have to destroy them before it is too late. Eventually, Erasmus is killed by one of the Anthropophagi and Dr. Wathrope determines that there is a monster infestation.
Meanwhile, Will remains perplexed about Dr. Wathrope, his motivations, and how he gained his own wealth. Eventually, Will and Dr. Wathrope enlist the help of a man named Varner, who they think will help them clear the town of Anthropophagi. Varner agrees and helps the two rid the town of the monsters because he feels responsible for the infestation.
The monsters wreak havoc on the town and its inhabitants, and Will, Dr. Wathrope, and Varner are initially powerless to do anything about it. Then, the trio enlists the help of a man named Kearns, who asks for money and total immunity. Dr. Wathrope quickly, but begrudgingly, agrees to Kearns' terms and they take on the monsters. Between the three, they kill over thirty monsters, leaving Will to kill the alpha (which in turn kills the rest of the monsters), thus riding the town of the scourge and causing Varner to extricate himself from the situation.
