Twenty-seven years after murdering the Forever King, the killer (Gabriel) waits for death in a high tower. During a storm, he observes a small procession approaching the château, recognizing their arrival as the signal his long wait is nearing its end. In the bailey, the château’s deathless inhabitants, including an Empress of Wolves and Men and her court, prepare to greet the visitors. A pale historian (Jean-Francois) beside the Empress glances up toward the killer’s tower. The killer watches his finale begin, reflecting on a past love and urging himself to have patience.

Historian Marquis Jean-François joins his mother, Empress Margot Chastain, at the gates of Sul Adair to receive guests who have arrived two nights early. The visitors are Draigann Dyvok, the new Priori of the Untamed, and his ragged court, come seeking vengeance. Draigann refuses to acknowledge Margot’s title, asserting his bloodline kneels for no one. Margot informs him she has summoned the leaders of the other great vampire houses for a summit to decide who will rule now that the Forever King is dead.

Draigann reveals he came because Margot holds Gabriel de León, the man who destroyed his house and murdered his mother. Margot promises Draigann he can witness de León’s throat being cut at the end. Draigann informs Margot that another expected guest, Kestrel Voss of the Ironhearts, is arriving much sooner than anticipated. After the guests are shown inside, Margot tasks Jean-François with urgently interrogating de León to learn the truth about his sister, the Grail, and why the sun has not returned, despite the death of Voss, believing this knowledge will give her advantage at the coming summit.

Jean-François enters Gabriel’s tower cell to find his thrall, Dario, nearly dead after being fed upon. Jean-François revives Dario with his own blood and sends him away before continuing to transcribe Gabriel’s history. Gabriel confesses that he is succumbing to the sangirè, losing his fight to avoid becoming the kind of monster he once hunted. Knowing Empress Margot needs his story completed before an impending Conclave—many of whom want Gabriel dead—he offers to tell the rest of his tale, including the Charbourg events and the final betrayal, but only if Jean-François arranges for him to watch his sister, Celene, die. Jean-François agrees.

Gabriel recounts his departure from Dún Maergenn after Dior’s funeral, unaware of her resurrection. Believing he has failed her as he failed his murdered daughter Patience, his sole purpose is revenge on Fabién Voss. Before leaving, he secretly drained three vials of Dior’s blood from her corpse, believing that anointing his enchanted sword, Ashdrinker, with it will make the blade capable of killing the otherwise invincible Forever King. He attempts to communicate with Ashdrinker, whose blade cracked fighting Voss. The sword is mentally fractured and accuses him of being a thief, but recovers the same night, weeping and apologizing. Gabriel notes the wounds Dior inflicted on him have strangely failed to heal.

Taking shelter in a ruined watchtower, Gabriel is ambushed by three wretched vampires. His silver tattoos fail to warn him because his faith died with Dior. Outnumbered and unarmed after dropping Ashdrinker, Gabriel is nearly killed but is saved by Baptiste Sa-Ismael, Lachlan á Craeg, and Aaron de Coste. Aaron, once a silversaint, is now a vampire (after the vampire Kiara, daughter of Nikita Dyvok killed Aaron, he was resurrected and held in thrall by Nikita). The three followed Gabriel from Dún Maergenn, refusing to let him face his quest alone. Gabriel reveals his plan to his friends to use the three vials of Dior’s blood to anoint Ashdrinker, wagering the holy blood will destroy the Forever King as it destroyed a Prince of Forever before.

The alliance of Gabriel’s friends is strained by animosity between Lachlan, a devout silversaint, and Aaron, now a vampire of the like Lachlan was raised to kill. Gabriel urges Lachlan to see that Aaron is the same friend from before his transformation, but Lachlan is wary of Aaron. Searching the rubble of the watchtower, they find Ashdrinker. Baptiste discovers a hairline fracture running from the sword’s broken tip and warns Gabriel that using the sword against powerful vampires will worsen the crack until it shatters. Baptiste can perform a forge-weld to halt the damage, but only in one of two forges in the empire: one in the capital, Augustin, and another in León. The group decides to travel to León.

The journey is tense. Lachlan’s hostility toward Aaron is a constant source of conflict, while Aaron grows irritable from vampiric hunger. Gabriel’s own sangirè worsens without alcohol to dull it. One night, a fight nearly breaks out, which Gabriel stops. Later, Baptiste follows Aaron into the woods and offers his own blood to calm his husband’s bloodlust. Aaron refuses, revealing his self-loathing for atrocities committed while enthralled to Nikita Dyvok. Fearing he would kill the man he loves, Aaron uses his Ilon-inherited Push or coercion—whispering “Fear it, love” and “Fear me”—to force Baptiste to flee.

After months of travel, the group reaches the Barony of León, Leon being the city of origin of Gabriel’s mother, Auriel. Since Auriel was turned out of Leon by her father soon after her pregnancy was discovered, Gabirel has never met his maternal family. Near the gates of Leon, Gabriel’s group spots a woman being pursued by wretched and ride to her rescue. She frantically warns them away, but the men proceed to attempt to help her, Lachlan falling into a hidden pit trap, injuring himself and killing his horse. The men realize the pursuit is a calculated snare. The woman and her soldiers use mechwork crossbows firing flaming quarrels to slaughter the vampires. She identifies herself as Charlotte de León, Gabriel’s cousin. She is openly hostile, condemning him for the disgrace he brought upon their family name because of his illicit origins and by betraying his vows and wedding a sister of his order, and declares his party prisoners.

Charlotte disarms Gabriel’s party and escorts them toward León. Her lieutenant Mathieu explains that twelve years ago Charlotte purged the city of three secret vampire covens by burning entire districts—an act that saved the city but earned her the name “The Ashen Lioness” and the resentment of the citizens. At the gates, Charlotte traps Gabriel, Lachlan, and Baptiste in the gatehouse, saying her grandfather, Baron Gerrard, will decide their fate.

Because vampires cannot enter a homestead uninvited, Aaron is imprisoned in the stables while the others are presented to Baron Gerrard de León during his 70th saintsday (birthday) masquerade ball. Gabriel is taunted by the court fool, Caspién, and his bloodlust nearly spirals out of control at the scent of a small cut on the fool’s finger. Gabriel requests permission to use La Forge de San Javon to repair Ashdrinker for his quest to kill Fabién Voss. Baron Gerrard agrees, telling Gabriel, “My house is yours” (77).

Gabriel has a disturbing nightmare of Celene and a red serpent. He is woken by a young maidservant, Odette, whose scent intensifies his bloodlust. He struggles to control himself and sends her away. Later, he and Lachlan go to the forge, where Baptiste is working with brilliant forgemaster Fernando Cortez. Baptiste is in awe of Cortez’s genius with mechwork weaponry. As they begin work on Ashdrinker, Gabriel observes how the common folk fear and scorn Charlotte despite her having saved their city.

The group attends duskmass at Le Dôme, the great cathedral of Leone Bishop Santiago delivers a sermon on love and forgiveness that connects with Gabriel. Afterward, Baron Gerrard meets with Gabriel privately, pressing him to accept his offer to become his heir. He promises Gabriel his mother’s journal if he accepts. Gabriel bursts out in anger against his grandfather, wondering how he dares make such an offer after years of abandoning him and his mother. Gerrard reveals that he sent several letters to Auriel, beckoning her back, but she returned them unanswered because of her pride. He hopes Gabriel is not undone by their family’s disease of egotism. 

On Gabriel’s way out, Charlotte surprisingly urges him to accept, admitting her reputation as the “Ashen Lioness” makes her unfit to rule. Back at the château, an agitated Aaron warns Gabriel that a deep evil permeates the city.

Gabriel and Lachlan return to the forge to find Baptiste and Cortez locked in a passionate embrace. Gabriel confronts Baptiste, who is unrepentant. He reveals that since being a vampire’s thrall he craves the “Kiss” and is furious that Aaron refuses to bite him. Echoing the bishop’s sermon, Baptiste frames his desire as love and, in his desperation, offers his bleeding knuckles to Gabriel to feed. Horrified, Gabriel refuses and orders him to finish mending Ashdrinker. Overwhelmed by his bloodlust, Gabriel rushes outside and nearly attacks a passerby. As cathedral bells ring, he heads back to the church, suspecting a sinister connection.

Inside Le Dôme before mass, Gabriel speaks with Bishop Santiago, debating faith and suffering. As they part, Gabriel shakes Santiago’s hand—pressing his silver sevenstar tattoo against the skin. Santiago’s eyes glint like cracking glass and he snatches his hand free, confirming he is under a vampire’s thrall. Knowing the city is in the grip of hidden evil, Gabriel finds Aaron in the stables, also in agonizing hunger, and kneels beside him to tell him something important.

After Gabriel tells Aaron about Baptiste’s infidelity and the city’s hidden evil, they devise a plan. They stage a violent public brawl to expose their enemy. Aaron genuinely feeds on a young guardsman—drinking three mouthfuls of real blood—before brutally fighting a furious Lachlan, who is not in on the ruse. During the fight, Aaron destroys several large angel statues outside the cathedral. Gabriel “drives” Aaron away by stabbing him with a borrowed sword, and Aaron flees the city. Gabriel then tells the Baron they will depart at dawn, creating a deadline to force their enemy’s hand.

Back in his room, Gabriel is again confronted by Odette, clearly influenced by an outside force to seduce him. He resists but is pushed to the brink by his bloodlust. In desperation, he breaks one vial of Dior’s blood and tastes it. The holy blood triggers a vision: a great red serpent coiled beneath León and a massive dark hand in the north reaching to extinguish the sun. The vision confirms the evil’s nature and apocalyptic scale.

Drawn by an irresistible pull, Gabriel walks through the silent city to Le Dôme. Inside, every citizen of León—including Baptiste and Lachlan—kneels in a silent trance. On the altar stands Ilon, one of the five original vampires and progenitor of the Ilon bloodline. Ilon has secretly controlled León since its founding, using sacramental wine at duskmass to keep the populace in his thrall or mind-control. He used Charlotte to eliminate rival vampires who had moved in during his century-long slumber. Now he offers Gabriel the city’s throne, intending him as his new puppet ruler, and commands Gabriel to drink his blood a third time to complete the thralldom.

Gabriel pretends to submit, but Dior’s blood has broken Ilon’s mental hold. He attempts to attack with his last vial of holy blood, but Ilon shatters it. Droplets splash onto several thralls in the front row—including Charlotte and Baron Gerrard—freeing them from Ilon’s mind-control. Just as Ilon overpowers Gabriel, Aaron crashes through a window, revealing their falling-out was staged. They attack, but Ilon uses thralls as human shields.

Charlotte stabs Ilon through the back but is struck aside before she can spark the blade’s flame. Baron Gerrard seizes the blade and twists the hilt to ignite it, whispering “One day as a Lion,” even as Ilon slices open Gerrard’s throat, killing him. As the ancient vampire burns, Gabriel recovers the now-repaired Ashdrinker and decapitates him. Charlotte is gravely wounded, but at Lachlan’s plea, Aaron saves her with his blood. Gabriel retrieves his mother’s journal from his grandfather’s body and reaffirms his mission to kill the Forever King.

In the present, Gabriel confesses he lost control and fed on Odette in a violent encounter before departing. He becomes enraged when Jean-François presses for details. The historian ends the session and descends to Celene’s cell, threatening her with fire to force her to tell her side.