At the Winter Trials, Morrigan talks with Cadence and shares her suspicions that Aunt Margot brought Morrigan into the Darling family because she wanted a Wundersmith to give the family status. Looking at the copyright of the book about her mother, Morrigan realizes that a company called Clark and Sons published it shortly after Morrigan came to Nevermoor. Francis reveals that the green vial contains a muscle relaxant that veterinarians give to Wunimals. Morrigan suspects that Aunt Margot has been trying to poison Lady Darling with the medicine. Just as the announcers at the trials share the news that Hawthorne Swift has been chosen to ride Alights on the Water Like a Seabird, an official asks Morrigan and Mahir to come with him.

Morrigan, Mahir, and Cadence are brought to Hawthorne and learn that he is unable to get Alights on the Water to obey his commands. He is supposed to be in the arena soon. Mahir helps Hawthorne to communicate in dragon tongue, but nothing works: Alights breathes fire and incinerates the barrel full of lure meat that Hawthorne has been trying to use as bait. Just before the gates to the arena open, Vesta Rinaldi enters the chamber wearing the red and gold uniform of the Rinaldi stables. The dragon responds to her commands. Vesta jumps in the saddle, locking in her mechanical chair, and takes flight.

The classmates realize that the lure meat smells like the same medicine being used to poison Lady Darling. They return to the Rinaldi box and watch Vesta and the dragon fly beautifully. Cosimo is shocked to realize his sister is riding the dragon. When she lands, he runs to her and hugs her. Vesta and Alights on the Water take first place in the event.

Miriam and Modestine put Morrigan in the swan dress that all the Darling girls wear for their debut. Margot asks if Morrigan will perform a bit of magic for them at the party, and Morrigan answers that she has something planned. After Morrigan’s aunts leave, Cadence says that she feels they are still missing something in their conclusions. Morrigan, however, is convinced that Aunt Margot murdered Dario. Cadence wonders if Dario discovered something about Aunt Margot. At the wedding, he made a joke about having a creative outlet that might have been directed at her. As Morrigan enters the party, Cadence gives her a paper with “Lady Horrible” written on it.

When Morrigan performs her magic, she summons Wunder to begin a series of transformations. First, she turns her dress from a swan into a crow, indicating the surname she prefers. She makes the ice sculpture swans take flight and then melt. She creates a golden dragon and has it fly about the room before turning it into the image of the Rinaldis’ dragon boat. Finally, she demands to know who killed Dario Rinaldi. Aunt Margot tries to interrupt, but Morrigan continues.

Cadence and Morrigan share their deductions with the room, first revealing that Vesta was riding the Rinaldi dragon during the Trials and had been training with Dario for some time. This prompts an argument between Vesta and her father about attending a dragonriding school. Finally, Vesta’s mother, Olivia, steps in and insists that Vesta be allowed to pursue this activity she loves and is quite skilled at: “Vesta has her own life to live, and I am going to watch her live it. All of it” (524). Cadence then reveals that Alights on the Water was being poisoned. Cosimo admits that he was being blackmailed to make the dragon lose the Winter Trials.

Morrigan reviews the note Cadence gave her and realizes that “Lady Horrible” is an anagram for “Hillary D’Boer.” She realizes that Aunt Margot must be the author of the Silverborn Saga. Now sure that Margot killed Dario (to cover this fact about herself up), Morrigan accuses Margot of murder. Cadence is exasperated that Morrigan is not following the script they developed, based on Cadence’s beloved mysteries, about how to conduct this final interrogation. Just then, Jack receives a burn paper that reads PLAN B.

Morrigan recalls that Plan B means that the task force has decided that Basking is not coming and that they must kill the Guiltghast. She wants to prevent this; after taking Jake, Louis, and Lottie aside, she explains the situation and then tries to summon herself to the Guiltghast like Squall taught her. However, the effort fails. Morrigan returns to the drawing room to find that Tobias is stirring up the crowd by ranting that Morrigan is not one of them. He claims that Morrigan attacked them and is going to destroy everything they love—that she is a danger to their peace and safety. Suddenly, a crash sounds from the Splendid Canal. The Guiltghast climbs over the fence and charges toward the Receiving Room.

The year is now Spring of Four. The Guiltghast breaks into the Receiving Room. Tobias shrieks that Morrigan has brought a monster into their midst. The Guiltghast reaches out a tentacle and grabs Tobias. Its body reflects his memories and shows Tobias confronting Dario on the bridge over the canal on the evening of the wedding. When Dario refuses to drug Alights on the Water so that Tobias can make money on a bet, Tobias threatens to expose Dario and Gigi’s love affair. Dario laughs and says that while he and Modestine agreed to wed to join their houses, both of them love other people; Modestine loves Sunny, and she knows Dario loves Gigi. The hope was that Rinaldi money could bring the Darlings out of debt. In return, the Darlings would vote to make the Rinaldis a Great House at the Silver Assembly.

Dario reveals that he knows that Tobias is from the Clark family and was formerly the publisher of the Silverborn Saga books, though Clark and Sons is now owned by Mr. Smithereens. Dario taunts Tobias about how everyone in the Silver District would turn against him if they knew Margot wrote those books. In a panic, Tobias grabs the broken tip of the tail of the dragon boat, stabs Dario, and pushes him into the boat.

When the memory concludes, the Guiltghast releases Tobias, who falls to the floor. The party guests turn on Aunt Margot, accusing her of being Hillary D’Boer. The Guiltghast seizes several people in its tentacles, lifting them high above the floor. One of them is Aunt Margot. Morrigan tries everything she can to stop the Guiltghast. It drops Aunt Margot, but before she hits the floor, the scene freezes, and Ezra Squall appears over a Gossamer bridge.

Squall observes that in her panic, Morrigan has once again invoked Tempus. Now, he says, she must decide what to do. He says that he can turn back time a few moments to try to prevent the destruction, but Morrigan is upset that this might mean Tobias will go free; she is also distraught about the decision to kill the Guiltghast, telling Squall that she doesn’t want to be a Wundersmith if it just means being an “exterminator.” Squall tells Morrigan that he sees her true self and says, “There is black ice at the heart of you. And you will need it for what lies ahead. THIS is the work of being a Wundersmith” (556). He explains that the Skyfaced clocks did in fact change over to Basking because the third disturbance, the waking giant, occurred. Morrigan thinks that this means the Guiltghast is the giant, but Squall doesn’t agree. They touch hands to summon enough Wunder to perform what needs to be done.

Time backtracks to Spring’s Eve of the Winter of Three. Morrigan finds herself in the moment right before she summoned the Guiltghast. She asks Jack to bring Lady Darling to the Receiving Room and asks Arch, her pickpocket classmate, if he can crack a safe.

It is now the Spring of Four. In the drawing room, Tobias is again ranting about Morrigan to the guests at her debut party. Morrigan agrees that she is not one of them. She accuses Tobias of stabbing Dario and coming back to the house to change his suit because he was covered in blood. Tobias asks the aunts to vouch that he was with them, but they do not. Morrigan guesses that when Tobias returned to the house, Lady Darling saw him covered in blood. Morrigan also guesses that Tobias begged Lady Darling for help but that she refused because he’s not Silverborn. Morrigan says, “It never mattered what you gave up, how much you dressed and talked and acted like them. Lady Darling was never going to forget where you came from” (564). Morrigan concludes that Tobias began poisoning his mother-in-law so that she would not reveal his crimes.

Morrigan then reveals that Tobias has been blackmailing Cosimo and that he tried to blackmail Dario first, killing Dario when he refused to comply. Morrigan reveals that Clark and Sons, Tobias’s publishing house, was sold to the Vulture, which horrifies Aunt Margot. Morrigan decides not to reveal that Aunt Margot is Hillary D’Boer. Lottie and Louis then enter with officers from the Silk, and Jack and Morrigan’s classmates lead Lady Darling into the room. Arch has the sharp tip of the dragon boat tail, which Lady Darling identifies as the murder weapon.

Morrigan returns to the Hotel Deucalion. Lottie and Louis visit her there, reporting that Gigi Grand has been locked inside Devereaux House since the wedding. Aunt Margot visits Morrigan as well. She tries to explain that while she did fight with Meredith sometimes, they also shared a bond: Margot began writing the Silverborn books to amuse Meredith. Margot now feels ashamed that she never spoke up when her parents treated Meredith as a traitor for running away. In revenge and to support the family, she started publishing the Saga, but she stopped after writing Gigi Grand. Tobias took over and wrote Madeleine Malcontent and the other nosedive books. Margot also admits that she once tried to enlist a friend’s help in bringing Morrigan to Nevermoor, though she knew her mother would disapprove. In response, Morrigan says that she has a real family: the people at the Deucalion and in Unit 919.

Morrigan enjoys her birthday party at the Hotel Deucalion and then meets with Jupiter. He reports that the Guiltghast has been fed and that Lam played her part very well. Morrigan finally confesses that she has been meeting with Ezra Squall. She explains to Jupiter how it feels to work with Wunder and how much she wants to learn. Jupiter is intrigued when she describes the Hush, explaining that though he is a Witness (someone who can see what others can’t), he could not use his gift around Morrigan while the Hush was in effect. He compares it to how it felt when Jack became a teenager: “[S]uddenly he felt like a closed book, and it took a long time to creak that book open again” (583). Morrigan shyly asks if she might consider Jupiter her uncle and practices calling him Uncle Jove when he agrees. Morrigan awakens the next day to find a print on her finger indicating that she has mastered another Wundrous Art.