At the start of the novel, its main character, Feyre Archeron, starts to grapple with her traumatic experiences in the previous novel in the series. Although she holds the prestigious status of High Fae, she is still scarred by her experiences. Meanwhile, she is still in a relationship with Tamlin, the High Lord of the Spring Court. At first, they had a healthy relationship; however, it becomes strained as Tamlin starts to be overprotective over Feyre and starts to control her. Because of this, Feyre's PTSD intensifies.
Despite this, a reprieve for Feyre comes with Rhysand, who is the High Lord of the Night Court. He recalls a bargain he and Feyre had struck years ago: in exchange for assistance, Feyre must spend one week per month with him. At first, Feyre doesn't like this arrangement. However, over time, she discovers that the Night Court is a safe place for her to explore herself and start her healing journey with the help of Rhysand's friend group, including Mor, Cassian, Azriel, and Amren.
As she spends more time away from the Spring Court, Feyre learns the kind of person that Rhysand truly is. They grow to respect, understand, and, eventually, love each other in a romantic sense. They pursue their relationship, and Feyre realizes that she is meant to be with Rhysand, not Tamlin, for the rest of her life. However, Feyre's life (and the lives of people around her) is threatened by the King of Hybern, who wants to conquer both the faerie and mortal realms.
To accomplish his goal of conquering both lands, Hybern needs to retrieve both halves of a book. That book, which is a powerful artifact, will allow him to break down the protective barrier between the two worlds. Feyre and her allies, however, think on their feet and quickly secure one-half of the book before Hybern can. But that doesn't make Hybern very happy, and he goes after Feyre, attacking everyone in her group.
Recognizing the impending war with Hybern, Feyre returns to the Spring Court. She decides to fake a reconciliation with Tamlin, still knowing that her true love is Rhysand. At the end of the novel, she reveals why she decided to go back to Tamlin: so that she could spy and gather information for the impending war.
