Eighteen-year-old Celaena Sardothien, the greatest assassin in Adarlan and the King’s Champion has a secret. She is really Aelin Galathynius, heir to the throne of Terrasen and part Fae. When she escaped her family’s assassination 10 years earlier, Celaena was taken in and trained by a master assassin. She hasn’t revealed her identity to anyone except Chaol, the man she loved and then gave up when he betrayed her.
Chaol knows that Celaena will be killed if anyone finds out she is Fae. He asks the evil king of Adarlan to send her to assassinate the royal family of Wendlyn, a nation at war with Adarlan. Wendlyn is the last stronghold of the Fae, and Chaol hopes Celaena will be safe there, abandoning her duties to the king and never return.
Chaol means well, but Celaena is anxious to find the Wyrdkeys, magical objects that wield tremendous power and can be used to open portals to other worlds. She reluctantly goes, but instead of going to assassinate others, she seeks out the immortal Queen Maeve of the Fae, her great-grand aunt, to get answers on how to destroy the Wyrdkeys.
When Celaena arrives in Wendlyn, she is despondent about the death of her best friend, Nehemia, and spends her days drinking, gambling and picking fights. As she staggers through the streets, she meets a Fae warrior, Rowan, who has been sent by Maeve to bring her to the Fae outpost of Mistward, just outside the city of Doranelle. Mistward is a haven for demi-Fae, most deemed not powerful enough to live in Doranelle. Celaena is wary of Maeve, but she needs answers about the Wyrdkeys, so she goes with Rowan.
Maeve promises to give Celaena what she seeks, but first the ancient queen wants to see what has become of Celaena’s Fae fire magic, which she hasn’t been able to use since the king obliterated magic in Adarlan. Maeve decides that Celaena will remain in Mistward until she trains with Rowan to master her gifts and control her magic.
In Adarlan, Prince Dorian seeks ways to hide his ice magic from everyone, especially his father. He accidentally loses control and uses his power in front of a beautiful royal healer, Sorcha, a young woman who has been secretly in love with Dorian for years. Sorcha vows to help Dorian and creates iron solutions for him to ingest, successfully dampening his magic. Sorcha and Dorian begin a romantic relationship.
Chaol, fresh with the knowledge of the king possessing a Wyrdkey and fearful for his best friend Dorian’s life, vows to discover how the king banned magic and discover how to free it. When Aedion, a general in the king’s army and cousin to Aelin Galathynius, comes to Adarlan, Chaol is disgusted that the man can serve the king who slaughtered his entire family.
Chaol quickly discovers that Aedion is secretly loyal to Terrasen and is working with the remnant of Terrasen’s nobles to free their country. Together, the group figures out that the king eliminated magic by using a triangular spell with three towers in distant parts of the land. They also discover that the king is breeding humanoid monsters on a remote island, with plans to launch a surprise attack on Wendlyn.
In the north, the king has recruited three rival witch clans to ride wyverns, dragon-like creatures, into battle for him. The clans are violent and competitive, barely holding themselves back from killing each other. Manon Blackbeak, heir to the Blackbeak clan and one of the fiercest witches, defies her grandmother and expectations by choosing Abraxos, a small but highly intelligent wyvern. While Manon has been trained to have no conscience, during a competition she saves the life of a rival, which earns the ire of her grandmother. Manon begins to question the ruthless hatred that she has been taught all her life.
In Mistward, Rowan is a cold and brutal teacher, using threats and violence to force Celaena to shift into her Fae form and bring forth her fire magic. At first, Celaena has no control but, eventually, she learns to shift between her human and Fae forms and summon her magic at will.
Celaena and Rowan become friends, and she helps him investigate strange murders of demi-Fae in the area. They discover that the Valg are committing these murders. The Valg are a race of demon creatures from another world that originally forged the Wyrdkeys. The Valg don’t have bodies so the king has been using demi-Fae as hosts to these creatures he summoned by using Wyrdkeys.
The Valg are the monsters that were being created on the island, and the king has snuck them and scores of soldiers into Wendlyn to attack and capture the demi-Fae for experimentation. The king’s army is headed directly toward Mistward.
With the threat of attack on their outposts, Rowan and Celaena prepare civilians for battle, but the attack comes sooner than they expect. While Celaena battles three Valg princes, Rowan defends the outpost from the rest of the army. Even in her Fae form and using the strongest display of her fire magic, Celaena is almost defeated until Rowan forms a blood bond with her that allows her to use his magic as well. Together they defeat the Valg. After the battle, they journey to Doranelle to get answers from Queen Maeve.
Maeve wants to see a display of Celaena’s power, but the girl demands answers first. Maeve tells her that the Wyrdkeys can’t be destroyed, only put back into the Wyrdgates, but no one knows how to do it. Maeve knows the king has at least one key and suspects that Celaena knows where another is. When Celaena refuses to admit that she thinks the third key lies in a family heirloom, the queen has Rowan brutally flogged.
Celaena uses a spectacular display of her fire magic to threaten Maeve, who stops the beating and orders Celaena to leave Doranelle without Rowan. Celaena reveals that she knows Maeve has wanted the Wyrdkeys for centuries and even killed the Fae warrior she loved, Athril, to try and get them.
Celaena holds the ring that Athril intended to give to Maeve before she killed him and uses it to bargain for Rowan. Maeve releases Rowan from his oath of service to her, and he immediately pledges an oath to serve Celaena. Rowan and Celaena leave Doranelle, and she makes plans to return to Adarlan to get the third Wyrdkey back.
News that Queen Aelin is alive and powerful enough to defeat of the king’s army in Wendlyn spreads rapidly. The rebels are filled with hope. The king is furious, and Chaol makes plans to quickly leave Adarlan, hoping to take Dorian and Sorcha with him, to keep them safe. Chaol thinks that destroying one of the towers will break the king’s spell, retuning magic to the land.
Before he tells anyone, he, Aedion, Dorian and Sorcha are summoned to the king’s chambers. They are questioned about a spy in the palace, and Aedion takes responsibility to save the others. He is shackled and taken to the dungeons to await execution, but Sorcha is the true spy, and the king knows it.
Dorian pleads for Sorcha’s life, but the king beheads her. Chaol draws his sword to fight, but Dorian, seeing the woman he loves dead and knowing his best friend is next, uses his powerful ice magic to freeze the room long enough for Chaol to escape. Dorian is captured. A Wyrdstone collar is put on his neck, causing him to be under his father’s control.
Celaena boards a ship bound for Adarlan. She wants closure in her relationship with Chaol and to find her former master, Arobynn. She believes Arobynn took an amulet from her neck, the amulet containing the third Wyrdkey, 10 years earlier, when he found her.
She insists that she must go alone. While Rowan isn’t happy about her decision, he concedes. Celaena plans on gathering her court and raising an army against the king so she can take back her throne in Terrasen. She will send for Rowan when the time is right.