Cinder -- Ever since the hover crash that killed her parents, Cinder has been a cyborg: a despised member of society, with little to no rights. She has no memories from before the surgery, which occurred when she was young. Now, 16-year-old Cinder works for her cruel guardian, Adri, and her two stepsisters as a market mechanic. When Prince Kai himself asks for Cinder's assistance in repairing a broken android, Cinder doubts that the matter is really one of national security. However, danger does seem to be on the rise as the Lunars (inhabitants of the moon Luna) with their mind-controlling abilities and deceitful glamours visit Earth for the annual ball. The Earth-Luna relationship has long been a rocky one, especially with cruel Queen Levana on the throne; everyone suspects she had the rightful king, queen and princess of Luna killed years ago in order to assume her sister's throne. Now, Levana seeks an alliance with the Commonwealth. Prince Kai is very aware that when his ill father passes on, he must become emperor and will likely have to marry Levana in order to maintain peace--a prospect he dreads. Tensions are high. The letumosis disease spreads and takes more and more victims every day, until Cinder experiences a loss herself; her kind stepsister Peony contracts the disease and Cinder herself is accused of being a carrier. In a fit of anger, Adri donates Cinder to the cyborg drafts which search for a cure to the disease by experimenting on these lesser members of society. Cinder expects that she doesn't have long to live; cyborgs never survive the drafts. But when her body fights off the disease and her tests come back with startling results, Dr. Erland suspects that Cinder is more than just a cyborg.

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Scarlet -- Since revealing herself to be a Lunar fugitive and learning that she is the lost Princess Selene, rightful heir to the Lunar throne, Cinder has been thrown into the New Beijing prisons. Dr. Erland wants her to join him in Africa where they can plot a way for her to take back her throne, but Cinder isn't ready for that. She wants to find the woman who helped save her from Levana's assassination attempt when she was a child. With a bit of help from dashing, highly-annoying, criminal mastermind Carswell Thorne, Cinder escapes her prison and journeys to France to find the Benoit woman. Simultaneously, Scarlet Benoit is infuriated that the authorities are entirely disregarding her grandmother's disappearance. When clues start to suggest that her grandmother was kidnapped by a pack of wolf-like men working to extract information about the lost Princess Selene, Scarlet resolutely sets out for Paris to track them down. Her guide is Wolf, a former member of the pack who has turned to street-fighting and seems to have left his old ways behind. But with the Lunars involved, nothing is as it seems.

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Cress -- Cinder, Thorne, Scarlet and Wolf are on the run. Thinking to employ the help of Lunar shell Cress, a girl who has been imprisoned in a satellite around Luna for years to be the queen's hacker, the group embarks on a rescue mission--only to have the operation go terribly wrong when Cress's captors pay a visit. Scarlet is taken prisoner on Luna, Wolf is in critical condition, and a blinded Thorne and helpless Cress are stranded in a desert far from all civilization. Cinder sees no option but to find Dr. Erland. Meanwhile, Kai continues to negotiate with Levana for the antidote to letumosis and a cease of the wolf-soldier attacks on Earth. As Cinder readies to return to Luna and start a revolution, Kai finds himself once again caught in a marriage alliance with Levana.

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Winter -- As the Lunars prepare for Levana's marriage with Emperor Kai and her coronation as Empress of the Commonwealth, Cinder and her crew begin their campaign on Luna. They have no idea whether the Lunars will believe Cinder is really the Princess Selene, ready to take back the throne and free her people from Levana's cruel and oppressive monarchy. Their plans quickly go astray, however, as first Cress is separated from their group and then Cinder and Wolf are taken to Luna's capital city. It is up to Princess Winter (the queen's stepdaughter), Scarlet, Iko and Thorne to rouse the outer sectors into rebellion. Levana, jealous of Winter's beauty and the people's love for her stepdaughter, orders Winter's guard Jacin to kill her. When he instead helps her escape to the outer sectors, Levana goes after Winter herself and poisons the lovely princess. It is a question of whether the others can get the letumosis antidote into the outer sectors in time. It is a question of whether Cinder and the rebellion can take back the Lunar throne before more blood is shed.