Starred Review It can now be said with assurance that The Monstrumologist series is a landmark of modern YA fiction. Even given the remarkable Printz Honor winning first book, who could have predicted the haunting, profound developments of the subsequent titles, none more so than this penetrating, devastating coda. Yes, there is a monster: the T. cerrejonensis, a dangerous reptilian creature thought to be extinct for 100 years. But the true monster is Will Henry himself, now 16 and becoming "the most aberrant of aberrant life forms." Though his upsetting maturation is logical, even inevitable, fans will be shocked to see their beloved Will surpass the cruelty of his master, Warthrop, as he fights, in gruesome manner, a crime organization for possession of the monster. Will goes too far; some readers might wonder if the author goes too far as well. This, however, is Yancey's finest hour, as he juggles , melds ree time frames and stares unblinking into humankind's darkest heart. It is a work of tremendous courage; both Yancey and Will are forced to consider the void: "The innocent perish. The stupid, the banal, the wicked ey go on and on." 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. HIGH-DEMAND BACKSTORY: Yancey's a big best-seller now, thanks to the The 5th Wave (2013), and all that new attention should rub off on this final volume in a critically adored series.

The Monstrumologist quartet wraps up in a haphazard, patchworked finale. Even though Yancey offers a tone-setting disclaimer via an "editor's note" at the forefront of the novel that the manuscripts he "translated" into this work were "nearly indecipherable, physically as well as contextually," fans will still come away ultimately unsatisfied--possibly even feeling cheated--by this disjointed conclusion. In the main narrative (there are at least three), Will Henry, now 16, often drunk and colder than ever, helps Monstrumologist Pellinore Warthrop track down the T. cerrejonensis, a giant, snakelike critter that poisons its human prey then swallows them whole. At the same time, the novel also fast-forwards decades later to 1911, when Will returns to care for an elderly Warthrop and then reverts back to when he was first taken in by his employer. All this makes for a confusing read, and the future plotline serves as a spoiler to the central narrative. Also inserted are broken stanzas of poetry and italicized rants on the meaning of love and life that connect at a much more simplistic level than the earlier books. Still, parts of the novel are quite exciting and will induce just as much stomach-turning if not full-on gagging. At the end, the results feel rushed, as if Yancey were trying to quickly finish the job. Even the relatively anemic page count implies it. A fizzling anticlimax. (Horror. 14 & up)

Gr 9 Up-After his parents died, William James Henry became the ward of and apprentice to eccentric Dr. Pellinore Warthrop. One of the last of his kind, Warthrop is a practitioner of "aberrant biology," a monstrumologist. During the years of his strange education, Will has been exposed to the monstrosities of both humanity and nature and has come to resent the mutually destructive nature of his relationship with his aging mentor. Unfortunately, his dissatisfaction could not have happened at worse time. There is a mysterious threat to Warthrop's career: an attempt to steal the last living specimen of a rare species with venom that could be used either as a destructive weapon or a powerful drug. This supernatural, noir-like thriller effortlessly builds intrigue as Will contemplates the past mistakes that have lead him to his current situation. The premise of the book is that Yancey is an editor who is trying to decipher Will's journals; he is unsure whether the incredible events he reads about actually occurred or if he is the victim of an elaborate hoax. This device makes the story less narrative and more contemplative, with many of its short chapters devoted to poetry and philosophy. Overall, Yancey's latest installation in the series is strong enough to stand on its own. Ryan F. Paulsen, New Rochelle High School, NY