A pair of witch sisters, Jana and Sabina, kidnaps a baby from her home and kills her parents. They believe the child will grow up to be the powerful sorceress that has been prophesized. Jana wants the witches to raise the baby, but Sabina murders Jana and takes the little girl to be raised by another.
Sixteen years later, Princess Cleiona Bellos of Auranos and her friends take a pleasure cruise to the impoverished nation of Paelsia to purchase wine, the country’s most notable export. While haggling with a wine vendor, Aron Lagaris, Cleo’s friend and suitor, gets into a disagreement with the vendor’s son, Tomas, and stabs him to death. In the ensuing melee, the princess and her entourage are quickly taken back to their ship by their guards and sent home.
Of the three countries in Mythica, Limeros to the north is cold and inhospitable; Paelsia in the middle is poor, dry and barren; and Auranos in the south boasts a temperate climate and is wealthy. Tomas’ death sparks an international incident as both Limeros and Paelsia hate Auranos’ wealth, and the people are angry that a privileged princess and her friends indifferently murder an innocent young man. Tomas’ brother, Jonas, seeks revenge and vows to start the revolution that Tomas wanted. Jonas aligns himself with Paelsia’s chief to change the lives of all poor Paelsians.
Back home, Cleo is horrified and disgusted that Aron killed Tomas. Her father, King Corvin, believes that Aron was simply protecting Cleo and announces that the pair will be engaged. Months before the trip to Paelsia, Cleo got drunk at a party and had sex with Aron, a decision she regretted the next day.
Since then, she has lived in fear of her father finding out — noble women are expected to remain virgins until they wed. Cleo hates Aron but she is careful not to upset him. She caters to his requests, fearing that he will reveal her secret. It was Aron’s idea to go to Paelsia to buy wine, as Cleo stopped drinking after the regrettable night with him. Cleo opposes the engagement, but her father is adamant.
Magnus Damora is heir to the throne of Limeros and son of the man dubbed the “King of Blood,” Gaius Damora. Gaius is ruthless and raised Magnus to be aggressive and to conquer. Outwardly, Magnus is cold; secretly, he is ashamed that he is in love with his sister, Lucia. Unknown to Lucia or Magnus, Lucia is the baby that was stolen from her parents by the witches.
Sabina is Gaius’ mistress, and both she and the king wait for the day when Lucia will come into her powers and help them find lost magical objects called the Kindred. The Kindred are four crystals that hold the purest essence of elemental magic: earth, fire, water and air. Gaius has plans to conquer Auranos because he thinks the Kindred are there. He publicly criticizes Cleo and Aron’s actions in Paelsia and partners with Chief Basilius to bring war to Auranos.
In Auranos, Cleo is under constant protection from her bodyguard, Theon, and is forbidden from leaving the palace due to the unrest in the neighboring countries. Cleo’s older sister and heir to the throne, Emilia, is gravely ill with a mysterious ailment that is slowly killing her. While the people of Auranos no longer practice magic, Emilia tells Cleo about an exiled Watcher in Paelsia who guards grape seeds infused with earth magic that have the power to heal.
Watchers are immortal sorcerers who dwell in the Sanctuary, a protected enclave beyond the mortal world. Once the Watchers could visit the mortal world in their immortal forms, but since the disappearance of the Kindred, they are bound to the Sanctuary, only able to travel to the mortal world through the dreams of mortals or in hawk form. If a Watcher takes human form in the mortal world, the person becomes mortal and trapped, unable to return to the Sanctuary.
With her friend Nic in tow, Cleo sneaks out of the castle. They go back to Paelsia to find the seeds that will save her sister. When he discovers Cleo missing, Theon goes to Paelsia to find her.
In Limeros, Lucia’s powers have manifested and are growing, but she is terrified of being found out and labeled a witch. She confides in Magnus, and together they practice her magic in secret. Sabina finds Magnus alone and offers him sex in return for Lucia’s secrets. When Magnus rebuffs her, Sabina tells him she knows about his romantic feelings for Lucia and that Lucia is not his blood sister.
Lucia walks in on Sabina threatening Magnus, and in anger, she uses her magic to burn Sabina to death. Instead of being upset about the death of his mistress, Gaius is thrilled that Lucia’s powers have manifested. He plots to use her in the war against Auranos. Gaius plans to storm the palace and use Lucia’s power to break the magical wards of protection.
Cleo and Nic wander through Paelsia, trying to get information about an exiled Watcher, but they fail. As they run out of money and time, an elderly woman named Eirene gives them a place to rest for the night.
Eirene tells Cleo and Nic about Eva, a powerful Watcher and sorceress who wore a ring that gave her the power to touch the Kindred and not be corrupted. Eva fell in love with a human hunter, and they had a child. Eva’s sisters, Cleiona and Valoria, were jealous and threatened the child’s life if Eva didn’t give them the Kindred, which would make the two sisters even more powerful. Eva brought the Kindred to the mortal world for her sisters and each took two, absorbing them into their bodies, transforming them into goddesses.
Since the Kindred were no longer in the Sanctuary, the sisters were trapped in mortal bodies in the mortal world. In anger, they killed Eva and eventually turned on each other. When the sisters killed each other, the Kindred reappeared in their crystal form. The hunter, who had worn Eva’s ring and watched, collected the Kindred and hid them.
When Cleo leaves the following morning, she asks Eirene for a way to contact her so she can send her a token of appreciation. Eirene gives Cleo a note in an envelope. Cleo has tried to be inconspicuous in her travels through Paelsia, but her distinctive looks and notoriety attract attention.
Jonas hears she is in Paelsia and tells Chief Basilius, who contacts Gaius in Limeros. Jonas kidnaps Cleo and imprisoners her. Magnus is sent to retrieve her for ransom for his kingdom, but before Magnus arrives, Theon finds Cleo and frees her. As they travel to a ship that will take them back to Auranos, Cleo and Theon admit they have fallen in love and they kiss.
Magnus and his soldiers find Cleo. Theon kills two of the guards, but Magnus stabs him the back and kills him. Nic hits Magnus in the head, and he and Cleo escape back to Auranos. Cleo is devastated.
Magnus returns to Limeros feeling defeated and expecting his father’s wrath, but Gaius is consumed with plans for the war and Lucia’s newfound powers. Lucia is the only person to offer Magnus support. Magnus reveals that they aren’t related by blood. He kisses Lucia and tells her that he loves her romantically. Lucia is disgusted and rebuffs him.
Cleo returns to Auranos, and while King Corvin is angry, he is relieved to have her home. Emilia’s condition has deteriorated, and the sisters spend time together. The united forces of Limeros and Paelsia march on Auranos.
Jonas is among them, but now he is questioning the motives of both King Gaius and Chief Basilius. The battle is fierce, hundreds die, and Magnus is gravely injured. Lucia uses her magic to save him and to breach Auranos’ walls so Gaius can seize the castle. She falls into a coma afterward.
In the castle, Cleo finds the note that Eirene gave her. It contains enchanted grape seeds. Eirene is the exiled Watcher that Cleo had searched Paelsia for. Cleo tries to save Emilia with the seeds, but it’s too late; her sister dies. Cleo finds her father, who has been injured in the fighting.
He tells Cleo that she is a descendant of the hunter and gives her Eva’s ring, which will allow her to hold the Kindred without becoming overwhelmed by the power. Corvin dies in Cleo’s arms. Then Cleo escapes the palace.
The Auranian forces are overpowered, and King Corvin is dead, so they surrender. Instead of splitting Auranos evenly as he agreed to do, Gaius slits Chief Basilius’ throat and takes all of Mythica for himself. He moves his family into the Auranian palace. When Gaius makes his first public speech to the kingdom, Cleo disguises herself and waits with the people outside the palace to hear the address. Jonas, who has left the Paelsian army, finds Cleo in the crowd. He tells her to be prepared for a rebellion. Magnus also finds Cleo in the crowd and captures her.