In Cinder, the plague, letumosis, is an epidemic for which there is no known cure. Because Prince Kai’s father, Emperor Rikan, has the plague, there is a national crisis in New Beijing. This alarms the neighbors because it will spread and destabilize the whole region. In a desperate search for the cure, cyborgs have been used for testing. When Cinder’s step-sister Peony contracts it, she is sent to quarantine and Cinder, who is part cyborg, is sent for testing. She soon learns that she is immune. Queen Levana intended to marry Kai in part to create an alliance with the Commonwealth, and Kai agrees for political reasons and because she gave him a plague antidote.
Through Dr. Erland, when Cinder learns she is Selene, she is confused about her origins and rather frightened of her responsibilities but he convinces her to embrace them. Prince Kai wanted Princess Selene, who is Queen Levana's niece, to occupy the Luna throne. Learning Cinder’s true identity, Kai broke off with Levana. Cinder is a threat because she has the knowledge and immunity, and is eligible to become the legitimate queen.
A rule to kill people who resist brainwashing is the worst kind of tyranny, However, Levana sees an advantage in that she knows Cinder/Selene cannot be brainwashed. Levana fears that Selene will take the throne, marry Kai, and eliminate her chances for political advancement.
Many possible parallels can be drawn to current society. Although most people are not princesses these days, Cinder’s circumstances in her step-family can be like those of many children living in abusive arrangements. When there are widespread social policies, such as killing those with independent minds, people unite in opposition and this can be a source of rebellion or building a democratic society, rather than monarchy.