Alina Starkov and Mal Oretsev flee Ravka aboard a Kerch merchant ship and land in the port city of Novyi Zem. Mal thrives aboard the ship while Alina is haunted by nightmares and longing for her power. They step ashore and pray for safety in the new world.
Alina and Mal have been hiding in the Zemeni town of Cofton for two weeks, working to save money for the frontier. When they return to their boardinghouse, the Darkling is waiting with Ivan and Grisha soldiers. One of his terrifying new shadow creatures - the nichevo'ya - bites Alina, and she loses consciousness.
Alina drifts in and out of consciousness aboard a whaler, kept under by Ivan's Heartrender power. Genya Safin tends to her while she experiences vivid dreams of Baghra and her childhood. When she wakes fully, she discovers they are at sea and demands to see Mal. The ship's captain, a privateer called Sturmhond, intervenes when Ivan mistreats her, and his twin crew members Tolya and Tamar defend her. Genya reveals the truth about Alina's intercepted letters.
The whaler enters the icy waters of the Bone Road. The Darkling reveals he wants Mal to track the sea whip - a legendary ice dragon - to create a second amplifier for Alina. He threatens to torture Alina if Mal refuses, and Sturmhond negotiates a week's reprieve. On the sixth day, Mal leads them to the creature, which surfaces in a spray of iridescent scales.
The crew harpoons the sea whip while Sturmhond orchestrates a mutiny against the Darkling. His own ship attacks, Ivan is killed by Tolya in a fierce duel between Heartrenders, and the Darkling is shot. Alina begs Genya to come with them, but Genya chooses to stay. They escape to Sturmhond's schooner as the Darkling unleashes a swarm of nichevo'ya, and Alina uses her power to hold them off as they flee.
Aboard the Volkvolny in the aftermath of the schooner mutiny, Sturmhond reveals he was outbid by another client and is delivering Alina to Ravka, not the Darkling. The sea whip is hauled onto the deck, and when Alina hesitates, Mal closes her hands over the harpoon and drives it home. Tolya and Tamar work seven iridescent golden scales free. Sturmhond leads the Sailor's Prayer for the thirteen crew lost in the mutiny, then sets a course for Os Kervo. He returns Alina's confiscated copy of the Istorii Sankt'ya, the children's book of Saints lives the Apparat once gave her, and points out that Sankt Ilya stands beside a sea whip in its pages. He hints that she should use the scales as a second amplifier. Late that night, alone with Mal at the prow, Alina opens the book to Sankt Ilya and they realise a third creature, a firebird, also appears in the illustration.
Alina and Mal study the illustration of Sankt Ilya in the Istorii Sankt'ya and discover evidence of a third amplifier - the firebird. They agree to seek all three of Morozova's amplifiers to defeat the Darkling. Sturmhond's Fabrikator seals the sea whip's scales into a bracelet, and Alina demonstrates the terrifying power of two amplifiers combined.
During the voyage south-east to Ravka, Alina practises her power at the schooner's stern and learns the stories of Sturmhond's rogue Grisha crew, many of whom fled the Second Army or Grisha Examiners. She trains in Zemeni combat with Tamar, while Mal takes daily thumpings from Sturmhond at the sabre. Sturmhond deflects every question about his real name or origins. Two nights later, Tamar wakes Alina before dawn fifteen miles off the West Ravkan coast. Sturmhond hands command of the Volkvolny to Privyet and the small party boards a hidden double-hulled craft called the Hummingbird. Squallers raise an updraft, goggles are passed around, and the sails snap out into vast wings as the schooner takes flight under the stars. Sturmhond bypasses Os Kervo and tacks inland, and as Mal and Alina realise where he is heading, he steers the Hummingbird straight into the Shadow Fold.
Sturmhond flies the crew into the Shadow Fold aboard a remarkable craft called the Hummingbird. Alina lights the way while the crew hunts volcra with devastating new guns. A vision of the Darkling causes Alina to drop her light, nearly crashing them. They land in a lake on the eastern side of the Fold, and Sturmhond removes his disguise - revealing himself to be Nikolai Lantsov, the second prince of Ravka.
Nikolai proposes a political marriage to Alina, which she refuses. She agrees to return to Os Alta and demands command of the Second Army in exchange for supporting his bid for the throne. Mal is furious and hurt by her decision, questioning his own place in her new life, but ultimately agrees to accompany her.
Alina uses her power to ferry supplies across the Shadow Fold on sandskiffs, then travels the Vy toward Os Alta with Nikolai's procession. They pass through the devastated town of Kribirsk, where church walls are covered with the names of the dead from Novokribirsk. Pilgrims flock to Alina, calling her a Saint, and Mal agrees to serve as captain of her personal guard.
Riding to Os Alta in Nikolai's coach, Alina is drilled in a stream of leadership maxims: meet insults with laughter, weakness is a guise, get them to follow the little orders. Nikolai also lets slip that he believes himself to be a bastard. In the village of Tashta, he yanks Alina into a public kiss to cement their supposed alliance, and Mal sees everything from horseback. That night they stay at Count Minkoff's dacha. In the sunken garden Alina gives Mal a golden sunburst pin for the captain of her personal guard and asks him to wear it. He pins it over his heart and they kiss, until Tamar interrupts: a group of dust-covered Grisha is at the gates demanding entry. Fedyor, who once saved Alina's life, has led a band of deserters from Sikursk to find her, and she decides to let them ride into Os Alta with the procession in the morning.
On the road into the capital, Nikolai's elder brother Vasily Lantsov rides out with around a thousand First Army soldiers in perfect formation to greet the returning prince. The brothers' first measured exchange is cool and probing; Nikolai disarms Vasily by greeting a rank-and-file sergeant by name and tempting him with talk of horses. The procession passes through the refugee tent camps outside the walls, then through the crowded, stinking lower town, across the canal into the serene upper town, and up to the Grand Palace. In the throne room, the frail King and prematurely aged Queen receive Nikolai with emotion. After a private family conference in which Nikolai reveals his Sturmhond identity, the King grudgingly grants Alina temporary command of the Second Army, with the threat of hanging if she is ever found conspiring with the Apparat. Mal is given a dishonourable discharge for desertion rather than execution, and walks out of the throne room ahead of her.
Alina enters the Little Palace and faces the remaining Grisha, who challenge her authority. Zoya Nazyalensky surprises everyone by supporting her. When tensions erupt, Alina nearly kills Sergei with the Cut but redirects at the last moment, splitting the golden dome instead. She takes the Darkling's chambers, and that night sees a terrifying vision of him standing in her room.
Alina convenes a war council, abolishes the separation of Grisha Orders, and orders Fabrikators into combat training. Nikolai sends Mal on a hunting trip to build alliances with the First Army. Alina visits Baghra and discovers the Darkling blinded his own mother as punishment. Baghra refuses to help find the firebird and warns that the amplifiers will consume Alina.
The war council discusses strategy against the Darkling and the mysterious nichevo'ya. Mal departs on a hunt with the royal trackers and nobles, and Alina meets with Botkin to arrange Fabrikator training. She joins Nikolai at defence briefings with the King's advisers and learns he plans to rebuild the Hummingbird as an escape craft. The Apparat's cult of the Sun Saint continues to grow.
Alina corners David in the Fabrikator workrooms and learns that Ilya Morozova was a Fabrikator who used merzost to create his amplifiers. She spends nights in the library researching Sankt Ilya while Tolya helps translate ancient texts. Vasily corners Alina in the woods with his own marriage proposal, which she deflects. She and Mal visit the chapel and find the triptych of Sankt Ilya, but the Darkling appears to her again in a haunting vision.
Summer deepens over Os Alta and Alina settles into the rhythms of leading the Second Army. Daily war-council meetings turn over intelligence on the Darkling's likely line of march from Fjerda or out of the Sikurzoi mountains in Shu Han, and on where the firebird might be found. Fabrikator-led combat training pays off: Materialki and Inferni work on flash grenades, and First and Second Army units begin to call themselves nolniki as they train together. Nadia's younger brother Adrik, a new Squaller, refuses evacuation to Keramzin and is allowed to stay and fight. At the training rooms, Zoya appears to watch Mal spar, and Alina confronts her about her loyalties. Zoya breaks, admitting she lost an aunt and a niece in Novokribirsk; Alina lets her stay. Mal then invites Alina to Adam Gritzki's fortune-telling party, promising to dress her as one of the Suli performers, and she agrees.
Alina, Mal and Tamar slip out to the Gritzki mansion in the upper town's canal district, disguised in Suli fortune-teller cloaks and red jackal masks. They blunder through fake fortunes for tipsy guests until a deliberate brawl erupts in the ballroom. Tamar tries to hustle Alina out through the garden, but in the dark Tamar is knocked down and Alina is dragged through a hedge into a courtyard adjoining the Convent of Sankta Lizabeta. The Apparat is waiting. He calls her Sol Koroleva, hints at a holy army of soldiers among the faithful, and claims that when the Darkling fled the Little Palace he left Morozova's journals behind, journals the Apparat now possesses. Before Alina can decide what to believe, Mal and a bloodied Tamar break in; the Apparat slips away into the dark. Back at the Little Palace, Mal confesses the cruel court gossip about them and that he has been staying away to shield her reputation, not because he wanted to go. They almost kiss, but a vision of the Darkling appears over Mal's shoulder and Alina flinches. Mal walks out. The Darkling lingers, brushes her hair from her neck and kisses her cheek with cold lips as she weeps.
Alina asks David whether the collar can ever be removed and learns it cannot be - breaking it would be catastrophic. David's mirrored dishes near completion while Nikolai outmanoeuvres Vasily in council meetings. An almost-kiss between Nikolai and Alina is deflected when he tells her he will not kiss her until she is thinking of him and not Mal.