Hello! You asked for a summary of the novel Cinder by Marissa Meyer. Cinder is the first volume in the Lunar Chronicles Series. It is a science-fiction Cinderella story, complete with an evil step-mother as well as two step-sisters.
The story starts out by introducing us to the main protagonist of the story: Linh Cinder. Cinder is a sixteen year old cyborg (a being with both organic and mechanical parts) who is the best mechanic in New Beijing, Eastern Commonwealth. She has a booth in the marketplace in New Beijing where she works with her android (a robot which resembles a human), Iko. Cinder currently lives with her step-mother, Linh Adri, and her two step-sisters, Peony and Pearl.
It's great being a cyborg: Cinder's body is equipped with a scanner which is linked to a net database. This means her internal computer can download personal information about anyone she meets. When Prince Kaito comes in to have his android, Nainsi, repaired, Cinder knows who he is before he even introduces himself. When her optobionics displays an orange light, Cinder knows that someone is lying. All in all, Cinder's pretty happy with being a cyborg. The only downside is that she has to keep her identity a secret. There is a social stigma to being a cyborg.
Chang Sacha, the baker across the street, is soon discovered to have contracted letumosis (the Blue Fever) and when someone shouts out that Sacha has the plague, the whole marketplace turns to chaos, with everyone running away and shopkeepers closing their stores. We soon discover that Prince Kai's father, the Emperor Rikan, also has letumosis. Events come to a head when Cinder's step-sister, Peony, also contracts the deadly plague. Linh Adri, Cinder's stepmother, blames Cinder for possibly infecting Peony with the fatal fever due to her supposed proximity to Chang Sacha; Adri maneuvers matters so that Cinder is forcibly transported to the palace, where there are labs for letumosis research. Indeed, cyborgs are being forced to participate in the search for a vaccine. There, Cinder meets Dr. Erland, a palace researcher, who is able to determine that Cinder is actually immune to the plague. He asks her about her childhood and discovers that Cinder was given mechanical replacement parts after an accident which killed both her parents. Her new guardian, Linh Garan, dies from the plague not long after adopting her.
When Prince Kai goes looking for Dr. Erland to find more answers about his father's condition, he runs into Sybil Mira, the head thaumaturge (the equivalent of an officer) in Queen Levana's lunar kingdom. Mira is at the palace to broker an alliance between the Eastern Commonwealth and the Luna. Prince Kai would rather Queen Levana's niece, Princess Selene, sit on the Luna throne, but Dr. Erland assures him that Princess Selene died in a fire when she was very young. Since only Selene's hand and a foot was retrieved from the fire, it is doubtful that she is still alive. However, Dr. Erland himself has been searching for the lunar heir for years. He knows that she is a cyborg.
Meanwhile, Cinder wants to leave New Beijing to escape from her step-mother's legal guardianship. Her step-sister, Peony, is now in the third stage of letumosis and is in quarantine; Cinder promises her that she will try to find an antidote. Emperor Rikan soon dies and Prince Kai is contacted by Queen Levana personally. She tells him that she will come to the Commonwealth herself and discuss an alliance with him. Impossibly beautiful, she has her eye on marrying the prince herself. When Chang Sacha also dies, Cinder observes that a med-droid takes out Sacha's ID chip.
When Cinder is invited to the royal ball, she is thrilled but also afraid. She turns the prince down, afraid that her identity as a cyborg will be discovered. In the end, Cinder discovers that she is the Princess Selene. Dr. Erland tries to persuade her to meet her obligations as heir. As the novel ends, Cinder cuts out her ID chip and resolves to meet Dr. Erland in Africa.
Thanks for the question. Enotes has a great chapter by chapter summary you will enjoy.