Following the events of A Court of Wings and Ruin, the faerie realm of Prythian finds itself in a state of tentative peace following the conclusion of a bitter war against the island nation of Hybern. During the war, the High Lords of the various courts of Prythian put aside their differences and joined forces to oppose the King of Hybern, who intended to destroy the magical wall that has long divided human and faerie lands, and to enslave the humans who live to the south of Prythian. Now, after the successful defeat of Hybern, life in Prythian is relatively peaceful. In the Night Court, one of several kingdoms that rule over areas of Prythian, Feyre Acheron struggles to adapt to her new reality. Formerly a human before she was transformed into a powerful faerie, she now sits alongside her mate, Rhysand, on the throne of the Night Court. As High Lady, Feyre must balance the demands of her personal life with her new responsibilities as leader. She dedicates herself to volunteer work in the city of Velaris while preparing for the Winter Solstice, an important holiday.  

Rhysand’s duties as High Lord of the Night Court often take him away from Velaris. Alongside Cassian, a member of Rhysand’s trusted Inner Circle and military commander of the Night Court, Rhysand travels to the camps of the Illyrians, a warrior-race that lives in the northernmost mountains of Prythian, which fall under the rule of the Night Court. Though Rhysand is half-Illyrian and half-faerie, and Cassian is a full-blooded Illyrian, there is long-standing tension between them and the Illyrians. Many Illyrians believe that during the war with Hybern, Rhysand deliberately placed Illyrian warriors in areas of the battlefield where they were likely to perish. Rhysand, for his part, regards the Illyrians as backwards, and he seeks to reform their society, which traditionally discriminates against females. He and Cassian seek to provide combat training for females, but the Illyrians push back against these reform efforts, and there is growing talk of rebellion, which worries Rhysand.  

Further compounding Rhysand’s problems is the undefended border between the human and faerie realms. The border lies in the Spring Court, the southernmost region of Prythian, and Rhysand learns that the High Lord of the Spring Court, Tamlin, has no troops left to secure the border. He travels to the Spring Court and confronts Tamlin, whom he detests. Centuries earlier, Tamlin’s father killed Rhysand’s mother and younger sister. In the fighting that followed, Rhysand killed Tamlin’s father and brothers, and Tamlin killed Rhysand’s father in turn. This is not the only source of his hatred for Tamlin, however. Previously, Feyre was engaged to Tamlin, who treated her in a controlling and abusive manner after a series of events that traumatized them both. Blaming Tamlin for Feyre’s unhappiness while she was living in the Spring Court, Rhysand allows his anger to get the better of him, and he insults Tamlin without making any progress to secure the border.  

Back in Velaris, Feyre, Rhysand, and their close friends and family prepare for the Solstice. After meeting a painter named Ressina, Feyre rediscovers her passion for painting and temporarily sets up shop in an empty gallery and studio, formerly owned by an artist named Polina who died in an attack on Velaris. Amren, Rhysand’s second in command, who was once a powerful ancient being before being bound to the form of a faerie, struggles to adapt to her new body. Mor, a powerful faerie and another member of Rhysand’s Inner Circle, talks with Rhysand about a deal he made with her long-estranged father, Keir, in order to secure Keir’s alliance in the war with Hybern. Now, Keir and his men will be able to visit Velaris, from which they were previously barred. Though she despises her father, who cruelly betrayed her in the past, she does not wish to show weakness by hiding from him. Nevertheless, Rhysand offers her a role that would keep her away from Velaris when Keir and his men are there. Cassian revisits the village where he was born and reflects upon his mother’s short and difficult life. Because she was pregnant outside of marriage, she was shunned by the village, which Cassian later destroys in revenge. Azriel, who serves as spymaster for the Night Court and is, alongside Cassian, an adopted brother of Rhysand, updates Rhysand on rumors of rebellion in the Illyrian camps.  

Feyre’s two sisters, Nesta and Elain, respond very differently to their traumatic experiences during the war with Hybern, including the death of their father. Like Feyre, they too have been transformed into faeries, but unlike Feyre, they were forced to transform against their will. Elain dedicates herself to gardening and cooking. Though she is in good spirits during the Solstice preparations, she has not yet fully accepted that she cannot return to her human life, and she ignores Lucien, formerly a prince of the Autumn Court, to whom she is connected by a mating bond. Though two faeries might be linked by a bond, they do not need to accept their mate as a partner, and Elain expresses little interest in Lucien, who now lives in the human realm with Jurian and Vassa, two human allies of the Prythian courts in their war against Hybern. Conversely, she expresses warmth towards Azriel, whose own feelings are unclear. Nesta, in contrast, has fully withdrawn from her sisters and spends her nights drinking in seedy bars. She only reluctantly joins the others for their celebration of Winter Solstice after Feyre reminds her that she and Rhysand pay Nesta’s rent. When Cassian offers to walk her home, Nesta rudely rejects him.  

In a private moment after the Solstice celebrations, Feyre and Rhysand winnow to their log cabin and Feyre announces her desire to have a child, delighting Rhysand. After a night of passionate lovemaking, Rhysand reveals that he has purchased land by the river in Velaris and contracted builders to construct a house according to Feyre’s preferences and designs. Later, he makes a second trip to the Spring Court and announces to Tamlin that he has requested for soldiers from the Summer Court to guard the border. Tamlin is despondent and alienated and takes little interest in Rhysand’s updates. Meanwhile, Mor retreats to her personal estate and makes a plan that she does not tell the others about.  

When Feyre attempts to purchase the studio from the family of Polina, they instead gift her the property and request that she donate the money to a charity that supports artists who are struggling financially. With the help and support of Ressina, she decides to reopen the studio and offer children in Velaris the opportunity to paint and express their feelings through art. After a month of planning and refurbishing, a group of children and their families arrive and paint in the new studio, some depicting their traumatic memories of the war. Meanwhile, Rhysand oversees the implementation of combat training for women in Windhaven. Though only a few young women show up for training, he nevertheless feels that he is making progress. Back in Velaris, Feyre and Rhysand walk together by the river and speak optimistically about their hopes for the future.