Princess Winter is the stepdaughter of Queen Levana, Luna’s despotic ruler. As a child, Levana was forced into a fire by her beautiful, older sister, Channary, where she sustained disfiguring burns. Levana learned how to use her bioelectrical ability (glamour) to project an image of herself to others and hide her true face to the world.
Cinder is Levana’s niece and the true heir to the Lunar throne. Levana tried to have Cinder killed in a fire when the girl was only 3 years old, but she was saved and smuggled to Earth. Cinder discovers that Levana plans to marry Kai, the emperor of Earth’s Eastern Commonwealth, and then kill him after she becomes empress. Kai wants to find the lost Lunar princess and encourage her to take back her throne, ridding the world of Levana.
Cinder tries to assassinate Levana but fails and ends up a fugitive. She is on the run with a group of other fugitives: another criminal, Carswell Thorne; Levana’s best computer programmer, Cress; one of Levana’s genetically mutated soldiers, Wolf; Scarlet, a girl who’s grandmother helped the toddler-princess escape from Luna; and Cinder’s friend and android, Iko. Cinder sets a plan in motion to start a revolution on Luna and reclaim her throne.
In an act of desperation to stop a war and get the cure for a Lunar-created plague that has been ravaging Earth, Kai agrees to marry Levana, but Cinder kidnaps him before the wedding. She takes him aboard Thorne’s ship and reveals that she is the princess. The kidnapping enrages Levana, who unleashes mutant soldiers on Earth. Cinder and Kai devise a plan to take Luna back from Levana, and the first part of the plan is for Kai to go through with the wedding. He contacts Levana and suggests the ceremony be held on Luna so Cinder and her friends can gain access to the tightly guarded moon. Levana agrees.
Levana is intensely jealous of her beautiful stepdaughter, Princess Winter. Winter has chosen to stop using her mind-control ability, a decision that has led to her mentally instability. Winter has frequent, vivid hallucinations, but remains kind and caring to the people of Luna, much to Levana’s ire.
Winter cares nothing of beauty, but is in love with her childhood best friend, a palace guard named Jacin Clay. Jacin had briefly defected from Levana’s service in an effort to help Cinder, but allowed himself to be caught so he could return to Luna to protect Winter. As a result of Jacin’s betrayal, Scarlet was captured, and Cinder’s group believes that Jacin double-crossed them.
After Jacin returns to Luna, Levana assigns him to be Winter’s personal guard, a position that both thrills and terrifies Jacin, who is in love with her. Jacin knows that if he reveals how much he cares for the princess, Levana will use this to blackmail and punish him, which is exactly what she does. After Levana’s head thaumaturge, Aimery Park, proposes marriage to Winter and she refuses, Levana orders Jacin to murder the princess. Jacin frees the imprisoned Scarlet and asks her to take Winter to the outer sectors of Luna where she can hide from Levana until Cinder reclaims her throne. Winter and Scarlet escape to Wolf’s hometown. Jacin then fakes Winter’s death.
When Kai’s ship lands on Luna, Levana suspects that Cinder is onboard. Guards search the ship and a fight ensues, but Cinder and her friends manage to escape and make their way to Wolf’s childhood home to enlist help from the people in Luna’s poor, outer sectors. Maha, Wolf’s mother, welcomes them, and they begin strategizing their revolution. The group reunites with Winter and Scarlet.
Cress hacks the Luna broadcast system and plays a videotaped message from Cinder, announcing her as Luna’s true queen and urging citizens to take up arms and join a revolution against Levana. The message is so effective that immediately after it plays, Cinder sees citizens in the town square beating up guards. She begs them to stop and save the fight for their true enemy, Levana.
Levana sees footage from the town square and sends soldiers to apprehend Cinder. Soldiers arrive, kill Wolf’s mother and capture Wolf and Cinder. The others escape. Afterward, Thorne and Iko travel to the palace to try and free Cinder and Wolf, while Scarlet and Winter go in search of Levana’s hybrid wolf army to convince them to fight against the evil queen.
The girls travel deep underground. They find the soldiers, who at first would rather eat the girls than help them. The soldiers are, however, surprised and impressed to meet Winter, a royal who refuses to use her abilities to manipulate and control others, sacrificing her mental health. They agree to fight for Cinder and their freedom, and remove Levana from the throne. Winter’s arrival in the soldiers’ barracks alerts Levana that she is still alive.
Winter, Scarlet and the soldiers travel from the tunnels to Luna’s lumber sector to recruit people to their cause. While the soldiers train the people, Winter battles hallucinations. Determined to kill Winter, Levana glamours herself as Jacin. She lures Winter into the woods, and then changes her appearance to that of an old woman who offers the princess apple candy. Winter eats the candy, which contains an aggressive, mutated form of the plague, and falls deathly ill.
Scarlet finds her in the woods and recognizes the markings of the plague. She takes Winter to the clinic, and the local doctor puts her in a suspension tank in an attempt to slow the progress of the disease. Soldiers take the tank out of the clinic into the open so people can see their beloved princess and lay flowers around her.
Back at the palace, Levana is irate with Kai for bringing Cinder to Luna, but she goes forward with the wedding. Kai dreads the wedding, and while he doesn’t know if Cinder is still alive, he has faith in her and her plan so he goes through with the marriage. During the reception, Levana brings Cinder from her dungeon for entertainment and for execution. Kai is horrified to see that Cinder is captured.
Levana isn’t wearing her veil. Since Cinder’s cybernetics aren’t affected by glamour, she records the queen’s face during the confrontation. Cinder declares herself the true queen of Luna and starts a fight. She escapes by jumping from the balcony into the lake below the palace. She almost drowns, but is rescued by Thorne, Iko, Cress and Jacin, who is now on the run since the queen knows that he faked Winter’s murder.
They take Cinder to a safe house, where they try to repair her badly damaged cybernetics and come up with a new plan to defeat Levana during the coronation. The group sees alerts that one of the outer sectors has been quarantined. They find video footage of Winter in the tank.
Cress and Thorne sneak into the palace as Lunar attendees to the coronation, while Cinder, Jacin and Iko break into the medical labs and steal the cure for the plague. After stealing the vials, they travel to the outer sectors and administer the cure to Winter, Scarlet and everyone else who is infected. Afterward, Cinder leads the rebels to the palace while Winter and Jacin travel to other sectors to gather support and fighters for Cinder’s revolution.
As Levana is crowned empress of Earth’s Eastern Commonwealth, Cinder and her rebel fighters arrive at the palace and demand the queen’s surrender. Levana and her thaumaturges engage the rebels in a bloody fight, using mind control to force many to kill themselves. Cress infiltrates the palace’s communication system, playing Cinder’s video, which shows Levana’s true face and hideous scars. The video unhinges Levana and the thaumaturges, causing them to lose control of the fight. Levana retreats into the palace, pursued by Cinder.
Winter and Jacin arrive with rebel reinforcements, but Jacin stops Winter from joining the fighting, fearing her fragile mental state. As he tries to take her away, Aimery shows up and uses his mind control to try to force Winter to kill Jacin, whom he has always seen as his competitor for Winter’s affection. In desperation, Winter uses her mind control to force Scarlet to stab Aimery to death. The act causes Winter to have a psychotic break.
Cinder finds Levana in the throne room, holding Thorne hostage. Cinder and Levana battle using mind control, until Levana surrenders. When Cinder goes to take a weapon away from her, Levana stabs Cinder in the heart. Cinder shoots and kills Levana. Cinder survives the stabbing and, in her first act as queen, gives Earth the cure for the plague, asks Earth’s world leaders to retract the laws that treat cyborgs as property and to allow Lunars to travel freely to Earth. They agree. Thone and Cress agree to help the government take the cure to different cities around the world.
Winter remains in the hospital for weeks following her breakdown. Not even a kiss from Jacin can wake her up. Finally, after an extended hospital stay, Winter becomes lucid enough to function. She volunteers to try a device that would suppress her abilities, which may help her mental illness. She also agrees to become a Lunar ambassador to Earth. Jacin vows to stay by her side. Scarlet asks Wolf to move back to Scarlet’s farm in France.
Cinder is crowned queen of Luna. Afterward, she tells Kai that she would eventually like to help Luna transition to a democracy with an elected government. At that time, she will step down as queen. He asks her if she would ever consider becoming his empress. She says that she would consider it, one day.