HAVING SURVIVED THE IMPERATOR'S cruel test and lashing, Lyr is more determined than ever to train as a soturion, and prove she deserves to stay in Bamaria. She now only has three months to prepare for the Emperor’s test in winter, and has agreed to additional secret trainings with her bodyguard and apprentice Still haunted, by her last interaction with the immortal Afeya, Mercurial, Lyr debates telling Rhyan his cryptic words to her, “You’re the fire.” But before she can, she is summoned by Arkturion Aemon for a trial.
Tani has been accused of being a member of the Emartis, the terrorist organization determined to replace Lyr’s father as arkasva with her Aunt Arianna. Many believe Arianna to be the rightful ruler, and identify themselves with black seraphim feathers—a symbol Tani recently had on her when she engaged Lyr in a fight. Lyr has been called as a witness, and believes Tani will be found guilty, but when the Imperator appears, Lyr is suddenly the one being questioned until she’s once more publicly humiliated and tortured. Fearing that Tani will tell the Imperator and Aemon her suspicions of Rhyan and Lyr’s affair, and illegal use of kashonim, Lyr defends Tani despite the damning evidence, and they are all dismissed.
Rhyan is furious he was forced to watch helplessly as Lyr was injured again and blames himself for what happened. Tristan arrives to see Lyr but finds an angry Rhyan who accuses him of physical abuse. Knowing the subject must be dropped before Tristan grows suspicious of her cuts and bruises— a result of Lyr hiding Meera's vorakh, Lyr ends the fight by lying to both Tristan and Rhyan—it’s the only way to uphold her blood oath and keep Meera and Morgana's forbidden magic secret—exposing the secret would mean death.
Rhyan tries once more to understand where her wounds have come from, and when Lyr won’t answer, he pulls away. Lyr later invites Tristan to be intimate in her apartment. But Tristan is also pulling away, sensing Lyr is keeping secrets. Knowing she can't count on Tristan's Ka to protect her, and feeling uncertain of her standing with Rhyan, Lyr looks deeper into the mystery of her missing power. The scrolls she believes hold the key have been returned to the Great Library by Mercurial. But Ramia, the half-Afeyan who gifted Lyr an ancient necklace, shows her the scrolls have been made unreadable and her research is cut short.
Rhyan mysteriously misses their first day of secret training but reveals he was summoned to the border to hunt akadim. The undead beasts have been growing in number, moving farther south, and for the first time in history, have been organizing. Rhyan and Lyr train, and the tension is smoothed between them. But they aren't the only apprentice and novice spending additional time together as Lyr finds Tristan's cousin, her friend Haleika, with her own off-limits apprentice, Leander. Haleika blackmails Lyr to keep her affair secret, or she’ll expose Lyr and Rhyan to Tristan.
Months pass and Valyati, the winter solstice, and the Emperor's final test are quickly approaching as Lyr's strength increases. But so is her growing attraction to Rhyan the more they work together. When an Emartis attack forces Lyr to stay at Rhyan's apartment for the night, the boundaries they'd so carefully constructed fall apart. Rhyan's intense nightmares force Lyr to intervene and wake him. She asks Rhyan to come to bed with her, just as friends, so they can both rest. Still emotionally raw from his nightmares, and a brutal night of fighting, Rhyan admits he can't. He presses her against the wall, admitting he doesn't trust himself, and almost kisses her.
But Lyr tells Rhyan how deeply she trusts him and finally he calms and they go to sleep. In the morning, Rhyan apologizes for his behavior, then suddenly, they're kissing until Aemon arrives to check in. She tries to forget the kiss happened as she attends the Days of Shadows celebration with her sisters and Tristan. But Lyr's worst fear comes to light as Meera begins having a vision. Barely making an excuse to leave Tristan, Lyr runs to Meera and pulls her from the party. Just before they can escape to safety, their escorts catch up to them along with Rhyan. To save Meera, Lyr finally breaks her oath, and tells Rhyan about the vorakh as they take off in a seraphim carriage.
Landing on Gryphon Island, Meera has recovered and takes off to calm down, while Lyr panics over breaking her oath. But Rhyan comforts her, and swears to keep her secrets. They walk the beach to find Meera, and run into Mercurial. Lyr's blood oath begins to burn, the magic punishing her for breaking the blood oath. Mercurial admits nothing can save her from the debt's final punishment unless the oath is changed. He also reminds her she should be wearing the necklace she received from Ramia. As he leaves, a storm hits the island. Rhyan and Lyr find Meera and run to their seraphim. As they fly home, the Emartis attack, upsetting the seraphim and Lyr is flung from the carriage, but saved by Rhyan. Until the blood debt is changed, her life will remain in constant danger, and her body in pain.
They arrive at Cresthaven along with all Bamarian nobility—there for security purposes during the terrorist attack. Lyr tries to conceal her pain and fear from Tristan, as they are briefed on the attack. Once dismissed, Rhyan alerts Lyr's father as to what happened. To save Lyr, her father makes his own deal with Mercurial, and the blood oaths vanish. Rhyan and Lyr agree to ignore their kiss, and focus on training for one more month. He also swears to keep the vorakh secret, and offers Lyr and Meera two illegal vadati stones from his mother, as tokens of his oath.
Lyr attends the Valyati ball, where the Imperator hints that Lyr’s cousin, Jules, suffered mistreatment with him before her execution, sending Lyr into a panic attack. She must be carried from the party to be calmed down by Rhyan. But after, Lyr can no longer resist Rhyan, nor can he resist her. They begin removing each other's clothing until Mercurial interrupts, finally forcing Lyr to make a deal in exchange for his silence. But before she can finalize the contract, akadim attack. Rhyan manages to kill one, but before he can get Lyr to safety another appears, and Rhyan has no choice. To save Lyr's life, he reveals he’s vorakh and travels Lyr to safety in a cave. They confess their love for each other before returning to Cresthaven. There they discover not everyone survived. Leander was killed by the akadim. The one Rhyan let live to save Lyr’s life. Haleika's soul was eaten by the beast, leaving her in the process of transforming into an akadim herself.
Heartbroken and full of guilt, Lyr is taken to the arena for the Emperor's test. To prevent her from using kashonim, Rhyan is bound by rope, unable to access his magic. Haleika is brought onto the field, just as she turns into a full akadim, revealing she is the test. Though horrified she must fight her friend, Lyr is determined to survive and protect Rhyan. But Haleika is too strong. She punctures Lyr’s necklace, breaking three of the red diamond centers as Lyr bleeds. To Lyr's surprise, she feels strength and power rush through her, and defeats Haleika. But before she can receive the Emperor’s pardon, the Emartis attack. Lyr's father is assassinated. Weak and in shock, Lyr faints.
She wakes the next day at Cresthaven. Though Meera is Heir Apparent, she has decided to abdicate rule to Arianna—knowing her vorakh will prevent her from being arkasva. Lyr attends the announcement, still grieving her father and friends. Tristan's grandmother pulls her aside, and tells her their engagement is off now that Lyr’s lost her status. Rhyan escorts Lyr outside to get some air and admits he needs some time alone. He feels he betrayed his oath as a soturion by saving Lyr, instead of killing the akadim. He feels responsible for Haleika and Leander’s deaths, but he has no regrets. He still loves Lyr more than anything. Mercurial arrives to finalize the contract just as Rhyan heads to the fortress walls for duty.
Mercurial demands Lyr find her magic power, and complete a favor for him. She agrees, and then Mercurial finally explains what saved her in the arena. Ramia didn’t give her a necklace, but an ancient piece of armor, one that belonged to, and contained the blood of the goddess Asherah. Lyr accidentally formed a kashonim with the goddess, when their blood mixed together. Not believing this is possible, Mercurial reveals it is because Lyr is the reincarnation of Asherah.
He puts the Valalumir star—part of the original light mixed with part of his soul into Lyr's heart, a process so painful she faints. When she wakes, she stumbles upon Arianna preparing for the announcement that she will rule Bamaria. Arianna covers up a tattoo of black seraphim wings. And Lyr finally knows that her aunt was the leader of the Emartis all along, and her aunt was the one who murdered her father.