A Vow so Bold and Deadly (cursebreakers, #3)

The third installment of the Cursebreaker series opens with two neighboring kingdoms on the brink of war. In Syhl Shallow, Grey, the newly discovered true heir to Emberfall's throne and a magesmith with magic in his blood, trains with Iisak, a winged, fanged creature called a scraper who is the king of Iishellasa and has sworn a year of service to Grey. Grey has given his half-brother Rhen, Emberfall's crown prince, sixty days to prepare for battle before Syhl Shallow's army moves against him. Meanwhile, Lia Mara, the young queen of Syhl Shallow, struggles to rule with compassion in a kingdom that expects cruelty. Her soldiers distrust Grey and his magic, and a growing anti-magic faction threatens her reign.

At Ironrose Castle in Emberfall, Rhen harbors a terrifying secret: Lilith, the enchantress who once trapped him in an endless curse, has returned. She threatens to send Harper, the girl from Washington, DC who broke the curse and now stands at Rhen's side, back to her world if Rhen does not win the coming war. Harper, who has cerebral palsy and has trained as a fighter, is unaware of Lilith's return. She wrestles with months of anger toward Rhen for torturing Grey and Tycho, a fifteen-year-old boy who had become Grey's devoted companion during his months hiding in Rillisk, when Grey refused to reveal that he himself was the missing heir. Harper chose to stay with Rhen rather than flee with her brother Jake and Grey, and the decision haunts her.

Rhen hosts a gathering of his Grand Marshals, the regional rulers and military leaders of Emberfall, to rally support, but the event turns hostile. The Grand Marshals accuse Harper of being a spy, questioning why the army her fictional kingdom of "Disi" promised never materialized. On the dance floor, Harper publicly confronts Rhen, declaring that Grey spent his life doing everything Rhen asked, and the first time Grey refused, Rhen had him strung up on a wall. That same evening, Rhen meets Chesleigh Darington, a mercenary who claims to cross freely between Emberfall and Syhl Shallow. She reveals that a thousand Syhl Shallow soldiers have already camped inside Emberfall's border, that an anti-magic faction exists in Syhl Shallow, and that weapons forged from Iishellasan steel are impervious to magic. Rhen, desperate for a weapon against Lilith, tells Chesleigh to name her price.

Rhen and Harper reconcile in the stables, where Rhen finally confesses that Lilith has been tormenting him for months, using Harper as leverage. That night, Lilith appears in Rhen's chambers while Harper sleeps in his arms. Harper awakens, seizes a dagger, and drives it into Lilith's midsection, pinning her to the floor. Lilith slashes Harper's arm before vanishing.

In Syhl Shallow, Lia Mara faces two assassination attempts by individuals who oppose her alliance with Grey and his magic. Grey heals her burns after the first attack and urges her to assert authority over her younger sister Nolla Verin, the former heir, whose habit of issuing orders on Lia Mara's behalf undermines the queen. Grey also faces deep resistance from the soldiers, particularly Captain Solt, who lost his twin brother fighting the monster Rhen once became. After weeks of tension, Grey visits Solt's quarters for a meal and dice, and their tentative truce begins to shift the army's attitude. Grey and Lia Mara grow closer and become lovers, their bond deepening alongside their political partnership. When Nolla Verin secretly dispatches troops to attack Emberfall before the sixty-day deadline, Lia Mara confronts her sister and rescinds the order, then strides onto the training fields to address her soldiers directly. Solt is the first to kneel, and for the first time, the army unites behind their queen.

Back in Emberfall, Rhen hires Zo, Harper's closest friend and former guard, as Harper's personal protector. Chesleigh delivers a dagger she claims is forged from Iishellasan steel, and Rhen takes Harper to Silvermoon Harbor to seek military support from the local Grand Marshal. The visit turns disastrous when hundreds of angry citizens confront Rhen, and Harper is pulled to the ground. Rhen rescues her, narrowly stopping one of his own guards from killing the Grand Marshal's young son. On the ride home, Harper persuades Rhen to seek peace rather than war, arguing that his conflict is driven by fear of Lilith, not by Grey or Syhl Shallow. Rhen agrees, framing his decision not as yielding to Grey but as yielding to Harper and to the possibility of a better path.

Before Rhen can act, Lilith launches a devastating attack. She appears in his chambers and mauls his body, destroying his left eye. When Dustan, Rhen's guard commander, drives a sword through her, she tears out his throat, unharmed by conventional weapons. Zo fires arrows, and a wound on Lilith's shoulder from what may be the Iishellasan dagger fails to heal. Lilith throws a blade that strikes Harper's thigh, and Rhen orders Zo to flee with Harper. As the two women escape on horseback, a winged creature tears Zo from the saddle, and Harper rides on alone, crossing beyond Ironrose's boundary where Lilith's power appears limited.

Harper rides for days to reach the Syhl Shallow border, where she is taken prisoner. After three feverish days in chains, Jake and Grey find her. Grey heals her infected wound with magic, and Harper begs him to help rescue Rhen from Lilith. Grey's advisors suspect a trap, but Iisak examines the dagger Harper brought and confirms it is Iishellasan steel by cutting Grey's hand, producing a wound his magic cannot heal. After Lia Mara quietly asks Grey if he wants to save his brother, Grey agrees to lead a small strike team to Ironrose, framing the mission as stopping Lilith rather than rescuing Rhen.

Grey takes a small force including Harper, Jake, Tycho, and Iisak into Emberfall. During the journey, the team is ambushed by Rhen's soldiers. Grey uses his expanding magical power to knock all the attackers unconscious and orders them left alive. Among the fallen, they discover that Chesleigh Darington is actually Ellia Maya, one of Lia Mara's trusted advisors who had been secretly fueling the anti-magic faction as a double agent. Grey sends a coded message to alert Lia Mara, who decides to lead her army into Emberfall to support Grey and pursue peace. She meets with Lieutenant Jamison of Rhen's border regiment, who acknowledges Grey's honor for sparing his soldiers, and the two sides open tentative talks.

At Ironrose, Lilith has killed nearly every guard and servant in the castle. Rhen spends days alone dragging corpses out for burning while Lilith torments him. She drops a breastplate and a mass of flesh before him, claiming it is Harper's heart, and Rhen believes her. She reveals that the Iishellasan dagger was her own plant, given to the spy for Rhen to use against Grey rather than against her. She has forged orders in Rhen's name commanding his troops to attack, and she waits in the castle to ambush Grey, the one magesmith who stands in her way.

Grey's team breaches the castle. In a darkened hallway, Rhen draws his sword but immediately drops it and falls to his knees, begging Grey to kill him. Convinced that Harper is dead, Rhen has nothing left to fight for. Grey grasps Rhen's hand and pulls him to his feet, telling him that a prince of Emberfall kneels to no one. Harper rounds the corner alive and tells Rhen she escaped and went for help. Grey addresses Rhen as his brother for the first time, urging him to rise because there is still a battle to be won.

In the confrontation that follows, Iisak crashes through a window and attacks Lilith in a fury, but she stabs him repeatedly with the Iishellasan dagger, fatally wounding him. Grey sets Lilith's skirts alight to create an opening, but she holds her ground. Rhen, wanting to spare Grey, asks Grey to curse him into the monster once more; with Rhen's willing consent channeling the magic, Grey transforms him, and Rhen-as-monster kills Lilith. Grey calls his brother back to himself, and for the first time the two embrace. Outside the castle, Solt's soldiers have captured a second scraper—Nakiis, Iisak's long-lost son, who had been enslaved by Lilith. Grey heals Nakiis's wounds, but the grieving creature refuses any alliance and flies away. Lia Mara arrives at Ironrose with her army, having secured a ceasefire with Rhen's border regiment through Lieutenant Jamison. With Lilith dead and both rulers willing to negotiate, the war gives way to peace. Grey invites Rhen to remain at Ironrose as his counsel, and the brothers begin to rebuild their relationship. Weeks later, Lia Mara discovers she is pregnant, a secret she and Grey keep hidden to protect their child from the anti-magic factions still active in Syhl Shallow.