Plot
On the last day of their first year in the Wundrous Society, the members of Unit 919 partake in a class called Containment & Distraction, as an intro to the harder class they will have to take the following year. Later, at a Wundrous Society meeting, one man asks for volunteers to lower the population of the Nevermoorian Scaly Sewer Beast, a species that dwells in Nevermoor and is approaching its breeding season. Thaddea volunteers for the task force, much to everyone else's surprise, and the leader of the group, Gavin Squires, and Holliday Wu from the Public Distraction Department, try to brainstorm ideas for ways to distract the non-Wundrous Society citizens of Nevermoor from the hunt for the beast so as not to cause a panic. Meanwhile, after returning to the Hotel Deucalion, Jupiter bakes her an intricate cake for not being able to tell her about Containment & Distraction and notes that they are approaching Christmas. Later, at the Christmas parade, Morrigan sees Hawthorne, and afterwards the two—along with Hawthorne's family—go home on the bus, on which Hawthorne's toddler sister, Baby Dave, causes trouble, and is attacked by a leopard Wunimal, called a Leopardwun. Fenestra picks Morrigan up and she senses her acting unusual. At a Christmas dinner, Dame Chanda Kali reveals that her favorite fashion designer was a Wunimal who looked similar, and the hotel staff–Morrigan included—begin to worry. Later, during her first day of school of the New Year, a new teacher, Rosenfeld, confronts Morrigan and takes her to the School of Wundrous Arts, where anyone can train in skills like Professor Onstald's to stop time, and learn about Wundersmiths.
Morrigan meets her fellow students, Conall and Sofia. Later, Morrigan is threatened by a rabid Bearwun and Dame Chanda Kali is attacked by a Horsewun. Morrigan keeps noticing a strange green light in their eyes as they go crazy. Dame Chanda explains that only a few decades ago, Wunimals were treated as less than human, as if they had the intelligence of a common house pet. In the Wundrous Society, Wunimals are warned of the virus that infects only them, causing them to act aggressively and become catatonic and "hollow," which is also dubbed "Hollowpox." When the society's condition worsens, Jupiter and Jack are put to work using their Witness powers to find infected Wunimals. Meanwhile, Unit 919 is forced to continue classes, with Morrigan retreating more and more often to the School of Wundrous Arts, where she finds a book, The Book of Ghostly Hours, where she can relive experiences and lessons of Wundersmiths of the past, who really weren't all evil. Unit 919's disruption and distraction classes, including What's That Behind You? and What's That Smell?, have been happening more frequently, and Morrigan later competes in a challenge in the class where they must go out into the city, and a) cause a panic, b) steal something, and c) don't get caught, during which Miss Cheery suggest that, Morrigan, Thaddea, and Mahir visit the Golbeian Library, which is really a giant library hidden in a pocket dimension.
While there, Morrigan plots to steal the first volume in the book series that Onstald rewrote, realizing that the unabridged version of the text is favorable to Wundersmiths. Morrigan and the others are attacked by insects that have emerged from a book, and while an elite team deals with them, Wunimal Colin becomes infected with Hollowpox. The children escape, but the librarian Roshni Singh is infuriated. Gideon Steed, an anti-Wunimal rights senator, begins pounding the Wunimals in the press, saying they should be locked up together or banned from city establishment, much to Morrigan, Jupiter, and the rest of the Hotel Deucalion staff's horror. When Morrigan accidentally reveals her Wundersmith abilities to the non-Wundrous Society public, Steed switches to her, provoking newspapers to claim that she is not an actual Wundersmith, and offers a large reward to anybody who can photograph her using her abilities. This leads Morrigan to spend more time in the School of Wundrous Arts, where she practices the Wundrous Art of the Inferno, and subsequently meets with The Kindling, a Wundrous deity, who dubs her a master. Upon returning to the school on level Sub-Nine of Wunsoc campus, Morrigan stumbles across Sofia, a Wunimal, infected by Hollowpox. When Fenestra reveals that she harbors Wunimals from the Wintersea Republic, Morrigan's home state, where they don't have rights, Morrigan begins to theorize that that is where Hollowpox originated, though Fenestra denies it. Morrigan travels to the Republic through the Gossamer, where she is found by President Wintersea, whose real name is Maud Lowry.
Lowry admits that her state has developed a Hollowpox cure, and promises Morrigan that she will try to distribute the cure across Nevermoor and the Free State. Morrigan decides to visit Crow Manor, her old house, and see her old stuffed rabbit, Emmett, being played with by Guntram and Wolfram, Morrigan's half-brothers. Gideon steed almost meets with Lowry, but doesn't and Morrigan learns from Squall, who comes to her, that Lowry actually commissioned him to create Hollowpox. He helps Morrigan eradicate the virus, even though she doesn't want to, and she almost dies due to exertion and the fact that multiple infected Wunimals converge on her in the moment. Morrigan wakes up two days later in the hospital, with everyone she cares about by her side, including Hawthorne, Cadence, Fenestra, and Jupiter. When she learns that more Wunimals are waking up as unnimals—normal animals—some are waking up intelligent, and some aren't waking up at all, she calls Squall to her. Squall tells her that there is no way to get the Wunimals back, but she refuses to believe him, and instead demands that he unmake the Hollowpox, as he was the one that made it. In exchange, she will become his student. Squall agrees, unmaking the Hollowpox. And Morrigan agrees to become his student, eager to learn more about the wondrous arts, signing a contract binding her to become Squall's student. Finally, she returns home to the Hotel Deucalion and rests.
