Young stadwatch guard Joost patrols Councilman Hoede's mansion, hoping to impress the Grisha Healer Anya. He witnesses a terrifying experiment in which Anya is given a drug called jurda parem that amplifies her powers, allowing her to control the minds of everyone present and command Hoede to harm himself.
Inej shadows Kaz and Jesper as they confront the Black Tips' lieutenant Geels at the Exchange over Fifth Harbour territory. Kaz outmanoeuvres Geels by neutralising his bribed rooftop snipers and threatening his girlfriend, exposing Big Bolliger as a traitor in the process.
Kaz is ambushed by a mysterious phantom who walks through walls and is brought before merchant Wylan's father, Jan Van Eck. Van Eck reveals the devastating power of jurda parem on Grisha and offers Kaz thirty million kruge to steal the drug's creator, Bo Yul-Bayur, from the Fjerdan Ice Court.
Inej eavesdrops on Kaz's conversation with Per Haskell, learning about a mysterious high-stakes job. Kaz offers her four million kruge to join the mission, revealing it involves near-certain death but extraordinary reward, and asks her to summon Jesper, Muzzen, and Wylan.
Kaz visits the House of the White Rose to recruit Nina, a Grisha Heartrender working as a mood-altering therapist. He tells her about jurda parem and reveals he needs her and Matthias Helvar, a former druskelle imprisoned at Hellgate who knows the Ice Court's layout.
Nina, Kaz, Inej, and Muzzen infiltrate the Hellgate prison's brutal gladiatorial arena. Nina watches in anguish as Matthias fights wolves, then helps switch Muzzen into Matthias' cell by disguising him with fake firepox while healing Matthias enough to move.
Matthias wakes to find Nina in his cell, and his rage drives him to try to strangle her before Kaz intervenes. Kaz presents the Ice Court heist plan and a pardon document, ultimately convincing Matthias to cooperate in exchange for clearing his name and the promise of returning home to Fjerda.
Jesper watches as the crew discusses the Ice Court's layout, with Matthias reluctantly providing details about the concentric ring structure, gates, and security. Nina reveals that Hringkalla is approaching, and Kaz devises a plan to enter through the prison and escape through the embassy, while Wylan is unmasked as Jan Van Eck's son.
Kaz distributes money and assignments to the crew, ordering preparations for departure the next night. When left alone with Matthias, the Fjerdan attacks him searching for his pardon document, but Kaz easily subdues him with his cane and demonstrates his sleight-of-hand skills as a warning.
Inej gathers supplies for the journey while reflecting on her past with the Dregs and her strained relationship with Kaz. She encounters Tante Heleen on West Stave, who threatens to reclaim her, before arriving at the harbour to find their crew waiting by the Ferolind.
The crew is ambushed at Fifth Harbour as their decoy ship explodes, but Kaz reveals a second Ferolind at berth twenty-two. Jesper fights his way to the real ship with Wylan, climbing the mast to provide sniper cover despite a bullet wound, while Wylan's flash bomb turns the tide of the battle.
Inej takes down multiple attackers from above during the harbour ambush but is stabbed by Oomen, the Black Tips enforcer. Badly wounded and losing blood, she nearly kills herself with her own blade before Kaz finds her and carries her to the schooner.
Kaz interrogates the captured Oomen, learning that Pekka Rollins hired the Black Tips and Razorgulls to stop them. After extracting the information, Kaz throws Oomen overboard and retreats below deck, haunted by the threat Rollins poses and determined to use the heist to begin destroying his nemesis.
Nina struggles to heal Inej's near-fatal knife wound using her limited Healer training, reflecting on her own abbreviated education and how she was captured by druskelle on the Wandering Isle. She monitors Inej through the night while Jesper reveals his own worry about the Wraith's survival.
The crew debates strategy aboard the Ferolind as Matthias reluctantly labels the Ice Court plans. Kaz devises a route through the prison's incinerator shaft and dismisses concerns about Pekka Rollins, while Nina checks on Inej and the crew argues over their approach to Fjerda.
Inej wakes after three days unconscious to find Nina at her side. They share a tender conversation about Inej's refusal to take the Dregs tattoo and how Kaz freed her from the Menagerie, before Inej admits she's uncertain whether Kaz visited her during her recovery.
Jesper grows restless on the voyage, sparring with Wylan over their respective skills while visiting the recovering Inej daily. When Inej finally emerges, Jesper escorts her around the deck, and she confides her worry about Kaz's obsession with Pekka Rollins while Jesper reveals his crushing gambling debts.