A cyborg named Linh Cinder is the novel's protagonist. She's sixteen years old and works as a mechanic, though most of her earnings go to her stepmother, Adri. Cinder has been told that at age eleven, she was in a terrible hover crash that killed her parents and necessitated the extensive surgeries that left her a cyborg. She was then taken in by her uncle Garan and left to his wife's care after his death. Adri and Cinder's stepsister Pearl resent her presence and look down on her, but her younger stepsister, Peony, is kind to her. Because cyborgs are considered second-class citizens, Cinder technically belongs to her stepmother, and Adri volunteers Cinder (against her will) for the medical trials being done to find a cure for the plague. Unbeknownst to the public, the medical trials for plague research are actually an attempt to find the lost heir to the Lunar throne: Princess Selene. The doctor conducting the trials discovers that Cinder is the lost princess, and she eventually comes to realize that everything she thought she knew about her parents and her life before the accident was a lie. Though she's extremely practical, capable, and compassionate, Cinder has few friends. She struggles with her self-confidence and fears rejection from others, going to extreme lengths to conceal the fact that she's a cyborg from those around her—especially Prince Kai. As she learns more about her past, Cinder becomes more self-assured and gains confidence in her abilities, culminating in a public stand-off with Queen Levana.
Prince (later Emperor) Kaito is the heir to the Eastern Commonwealth. He's a popular, handsome young man who meets and befriends Cinder when he takes his android to her for repair. He eventually falls for her and, not realizing she's a cyborg, invites her to the royal ball. Kai is kind and willing to do anything to protect his people. He even agrees to marry Levana—and forfeit his own life in doing so—to procure an antidote for the disease that is ravaging the Eastern Commonwealth. Kai genuinely cares for Cinder, but he feels shocked and betrayed when it is revealed at the ball that Cinder has been concealing the fact that she is both a cyborg and a Lunar. In the aftermath of the ball, Kai turns Cinder over to Queen Levana, who insists on putting Cinder on trial. Cinder manages to break out of prison at the end of the book, and Kai is left unsure as to whether his feelings for her are real or the result of her Lunar powers of manipulation.
Queen Levana is the Lunar queen and the one behind the letumosis plague. Cruel and powerful, Levana assumed the throne after her sister (the direct heir) and her niece, princess Selene, died under mysterious circumstances. In addition to having strong powers of mental manipulation (which she uses to make others find her beautiful), Levana also commands a formidable army and poses a serious threat to Earth, which she clearly wishes to rule. She travels to Earth to give Kai a sample of a letumosis antidote the Lunars have developed (conveniently, it's come just a little too late to save his father). She uses the antidote as a bargaining chip, informing Kai that he must marry her before the Lunars will produce the antidote for the Commonwealth. Desperate to save his people from the plague, Kai agrees, even though he knows Levana intends to kill him and invade Earth.
Dr. Dmitri Erland
Dr. Erland leads the royal plague research team in the Eastern Commonwealth. He is introduced to Cinder when she is "volunteered" for plague research by her stepmother, Adri. He is intrigued by Cinder's cyborg structure, which is much more extensive and sophisticated than Cinder initially realized. When Cinder displays an immunity to letumosis, Dr. Erland negotiates with her: she agrees to continue cooperating with the research program on the condition that Peony will be among the first to receive any antidote they produce. After conducting further tests, Dr. Erland...
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