A Court of Wings and Ruin

The endgame kicks off once the Wall between Prythian and the human lands is destroyed by the Cauldron and Hybern launches its full invasion. The High Lords, now uneasily allied thanks to Feyre and Rhysand's diplomacy, muster their armies alongside human forces brought by Feyre's father and the ships of Miryam and Drakon. Tamlin, Beron, and even Elain's former fiancé Graysen arrive to fight on Prythian's side, tipping the battle. Nesta's newfound power lets her sense the Cauldron's location and warn Cassian moments before the Illyrian legion is slaughtered by its unleashed force.

In the chaos, Amren betrays Feyre and seizes the Cauldron for herself, explaining afterward that she meant to use it to free herself from her Fae body and return to her true, ancient form, even knowing it would make her a mindless destroyer with no memory of her friends. Before she can complete the act, the Cauldron drags Feyre to where Nesta and Elain are facing the King of Hybern, who is holding their father captive. Cassian tries to intervene but is badly wounded, and the King kills Feyre's father. Elain then drives the blade Truth-Teller into the King's throat, and Nesta finishes him by cutting off his head, ending Hybern's threat for good.

With the King dead, Feyre realizes the Cauldron itself is the source of all life and magic and must be restored rather than destroyed or misused. Rhysand offers himself as the conduit to channel its power and seal it properly, but the strain of the act kills him. The surviving High Lords combine their power to resurrect him, and in the same act Rhysand manages to pull Amren back from the brink of losing herself entirely, saving her life and her memories. Lucien returns from his search having found Vassa, a cursed mortal queen who turns into a firebird each night.

In the aftermath, Feyre asks Miryam and Drakon to hide the now-quiescent Cauldron on their secluded island, out of reach of anyone who might misuse it again. She calls for a new treaty to reorganize relations between the human territories and the Fae courts, formally ending the old, unequal order. The book closes with peace settled over Prythian: months later, in an epilogue, Feyre and Rhysand hold a wedding ceremony recognized by all the courts, a symbolic capstone to the war and to Feyre's transformation from mortal huntress to High Lady of the Night Court.

As book four opens, Hybern's war is over: the King of Hybern is dead, killed by Elain and Nesta together, and the Cauldron — the source of all Fae magic — has been recovered and hidden away on Miryam and Drakon's island rather than destroyed. Feyre openly stands as High Lady of the Night Court alongside Rhysand, a status now known and accepted by the other High Lords after it was revealed during a confrontation with Eris and the Autumn Court heirs on a frozen lake in the Winter Court.

Feyre's father died during the final battle, killed by the King of Hybern while held captive. Rhysand died sacrificing himself as a conduit to restore the Cauldron's power safely, but the High Lords combined their strength to resurrect him; in the same act, Amren was pulled back from a self-destructive bid to free herself from her Fae body after she betrayed Feyre by seizing the Cauldron mid-battle. Amren survives, still bound in her Fae form, her true ancient nature unresolved.

Feyre's sisters have been transformed by the Cauldron: Nesta remains bitter, traumatized, and emotionally isolated after the war, resistant to closeness with anyone including Cassian, despite having saved his life by warning him of the Cauldron's attack. Elain has developed seer abilities and has a mating bond with Lucien, though she has not embraced it and her human fiancé Graysen rejected her once she became Fae (though he later fought alongside the Night Court in the final battle). Lucien, having left the Spring Court for good, found and rescued Vassa, a mortal queen cursed to transform into a firebird nightly, and remains torn between his feelings for Elain and his search for answers about his parentage — it's suggested Helion, High Lord of the Day Court, may be his true father.

Tamlin, having lost most of his people's respect after his alliance with Hybern was exposed, ultimately fought on the side against Hybern in the final battle, but his relationship with Feyre remains fractured and unresolved. Mor revealed to Feyre that she does not love Azriel romantically and prefers women, leaving Azriel's long unspoken feelings for her unreciprocated and unresolved. The Bone Carver, Bryaxis, and the Weaver all aided the Night Court in the war after being bargained with by Feyre and Amren.

The book ends with the beginnings of a new treaty being negotiated between the human territories and the Fae courts to establish more equal relations, opening a new, peaceful era for Prythian.