The book begins with us learning of a girl named Cress. She is our modern day Rapunzel, stuck in a ship that is revolving around Luna, alone except for the occasional visit from Sybil, Levana's favorite thaumaturge.
We find out that Cress was to be killed for being a "shell", a Lunar without any persuasive powers, but Sybil discovers that Cress is the best hacker around after Cress hacks her way into the Lunar's database to help her fellow cellmate find his parents. They find them and he sends them a message, but his parents turn him in to the Royal Guard and he is executed. Sybil takes Cress and begins asking her to hack different things and soon places her on the ship that is orbiting Luna by herself to be Levana's hacker.
Unknown to Sybil though, Cress has heard that Levana plans to kill Kai after marrying him and Cress is instead helping Cinder and Thorne (who she has fallen in love with through newsfeeds) by scrambling all signals that could have them identified by Lunar ships that are searching for them.
Cinder contacts Cress via com to ask Cress to show all the evidence on the surveillance tapes she has of Levana to the world to show what a bad person she is, and Cinder says that if the world sees this they'll never condone this wedding between Levana and Kai.
Cress says she will, but is hesitant knowing that Levana will kill her for this treason. When Cress tells Cinder she's not on Luna but instead in isolation on the small ship, Cinder and Thorne agree to come rescue her.
Thorne takes a pod to Cress's ship, not knowing that Sybil has come back and has tied up Cress and is laying in wait. Sybil overpowers Thorne and ties him up with Cress and sets their escape pod to self destruct and releases it, then Sybil and her guard take the pod from back to Thorne's ship so she can capture Cinder.
Cinder, not knowing that it is Sybil on the pod, opens the door and Sybil captures her and almost kills Wolf, but Sybil's guard turns on her. Cinder, the guard (named Jacin), and Wolf escape, but Scarlet is taken prisoner by Sybil and glamoured into piloting Sybil's ship now that she's been hurt.
Meanwhile, Thorne and Cress have managed to disable the self destruct on their pod and land on Earth in a desert. Thorne is blind due to hitting his head when they landed. Cress leads him across the desert to try to find civilization, and after miles and miles they finally come upon a trading caravan that takes them in. Cress is out for a few days because she has formed an infection in her feet due to the blisters from all the walking. When she comes to, they go with the caravan to the nearest city.
Cinder and Jacin take Wolf to Dr. Erland to see if he can help him. When they arrive, Cinder is surprised to see that the whole village treats her like a savior and are eager to help them due to what Dr Erland has told them; that Cinder will continue to stand up to Levana and will one day assassinate her.
The caravan pays for a hotel room for Thorne and Cress, who are posing as a married couple who are on honeymoon and were robbed, and Thorne goes downstairs to gamble to win an escort droid to give to Iko (Cinder's caregiver who is now the control system of Thorne's ship until they can get a new body for her). Cress doesn't realize that's what Thorne is doing and all she sees is him in the bar gambling with a beautiful girl on his lap, so she readily goes with one of the caravan people to go have dinner with them. They've lied though, and realized she's a shell and are taking her to "a doctor in the desert who pays good money for shells" and so they kidnap her and Thorne has to find her.
When they arrive at the village where the Dr is, they take Cress to him and it is Dr Erland. He seems in shock when he sees her and pays the caravaners for her and takes her blood sample. She hits him and escapes but only goes a few doors down in the hotel and hides in a closet, knowing the caravaners haven't had time to leave yet. She waits for a while and doesn't hear the Dr coming after her, so she sneaks into a room that has a netport so she can try to contact Thorne at the hotel.
It turns out Wolf is in the room she sneaks into and he grabs her and holds her hostage. Dr Erland comes in and tells Wolf to let her go, and Thorne shows up about the same time. It's pretty hilarious because they all don't know each other for a few minutes until it gets straightened out (Wolf has been in a coma and doesn't remember Erland, Cress doesn't know Wolf since she's only been with Cinder and Thorne this whole time, Thorne is currently blind so he doesn't see who Cress is screaming about and threatens to shoot everyone....good times). Once it's all straightened out, Cress tells Thorne that they need to leave because the town they were in has figured out they are the wanted fugitives and are coming after them. Iko lets Cinder know military are on their way about the same time and she rushes upstairs to find everyone there. They all try to escape, Cinder telling the others to go on without her for now while she tries to convince Wolf to leave with them. He has hidden himself in grief once he realizes again that Scarlet has been taken hostage by the thaumaturge.
Cinder takes control of Wolf's mind once she realizes nothing is dragging him out of the building and makes him come outside with her. The military has already surrounded their ship and forced them to surrender. Erland begins controlling the few guards closest to them, but they can't control all of them and they know they are doomed.
Suddenly, all the townspeople show up and surround them. The military tell them to back off, not realizing most are Lunar, and the townsfolk take control of the remaining guards making them turn on each other, and Cinder and the rest escape.
After escaping, Cinder tells them her plan since Dr Erland has convinced her that trying to out Levana at the wedding is a bad idea due to the fact that she's a wanted criminal and nobody will believe her.
Cinder has decided to go to Earth and kidnap Kai instead of outing Levana so that the marriage won't go through, and then they are going to head to Luna to convince the Lunar people that Cinder is the rightful queen and overthrow Levana. Everyone agrees and they head to Earth.
Cinder goes to her stepmother's house under glamour as a guard and tells her that she has their royal invitations. Her stepmother says they've already received their wedding invitations, and Cinder acts like there's been some mixup and asks to see the invitations they received. Once she does, she glamours them to look like they are for someone else and glamours some napkins to look like invitations with her aunt's name on them. She gives those to her aunt and takes the real invitations to use to get into the palace.
In the meantime, Cress and Wolf are posing as guests and head into the wedding reception. They sneak to the security room and disable all cameras. Cress also disables all hidden Lunar cameras that she knows are in the building.
Iko, with her new escort droid body, poses as a servant and enters the party that way and opens the hatch in the underground tunnels that Dr. Erland, Thorne, and Cinder are sneaking in through.
Cinder and Iko head to kidnap Kai, and Erland and Thorne head to the medbay so that Erland can fix Thorne's temporary blindness. Once there, Erland realizes after seeing a bruise on his arm that he has contracted the plague and locks himself in a quarantine room and tells Thorne to go find the others.
Cinder enters Kai's room and ends up having to tranquilize him with one of her darts because he won't come willingly, and they all meet back up at the medbay. Dr Erland tells them that he has figured out that the Lunars are the ones who started the plague to begin with, since he has put two and two together from what Cress has told him about the thaumaturge's taking all shells when they're born. He knew they were working on a cure, but realizes that the shells were being taken and experimented on before the plague ever started, which means the Lunars knew what was coming and had taken precautions.
We also find out that Erland is Cress's father, and he never wanted to give her up to Levana and the thaumaturge, but he thought they killed shells because they were of no use, not that they locked them up and experimented on them and took blood samples to make the plague. He tells her he had no choice but to give her up and he still loves her and thought about her every day.
After the speech, Erland tells them to go and leave him behind and they head for the roof, where Jacin is supposed to be waiting with the ship. Instead it is thaumaturge Sybil and her guards. Cinder manages to take control of Sybil while she is distracted with controlling Wolf to make him kill Cinder (he also snaps Iko's neck in the fight) and makes her go nuts and jump off the roof. They manage to take down the other guards, Wolf regains his senses, and they escape.
One of Levana's other thaumaturge's goes to her and lets her know what's happened and says they've captured Jacin and Dr Erland is in the quarantine room. Levana goes to Erland and with his dying breath he lets her know that the true queen will soon overtake her. Jacin claims that he was working as a spy for them the whole time and he is the one who told Sybil where the ship would be. Levana doesn't believe him but agrees to take him back to Luna for a trial.
The story switches to Scarlet, and she has been placed in a large cage as a pet for Princess Winter alongside a caged wolf after Levana tortured Scarlet to try to get information about Cinder's wherabouts and Levana forced Scarlet through glamour to cut off her own pinky.
Before it could get any worse, Winter asked Levana, her mother, to let her have the human as a pet to practice her glamour on.
Winter tries to convince Scarlet she is a friend, but Scarlet doesn't trust her and accuses her of glamouring her since Winter looks so beautiful and that if she can't even drop her glamour, then how is she supposed to trust anything about her. Winter tells Scarlet she hasn't glamoured anyone or anything since she was 12 years old and she is there to help. She leaves Scarlet some candy, and when Scarlet eats it since she is starving, she realizes Winter may be telling the truth since the candy had pain medication in it.
Onboard the ship, Kai has awoken and goes to find Cinder. She finally tells him that she is Princess Selene and that they are headed to Luna to take down Levana and she needs his help to do it. He kisses her, but in the middle of the kiss Cinder sees in her newsfeed that Levana has already declared war on Earth and has killed everyone in the village that helped Cinder and Dr Erland and is proceeding to attack other places too. They know they must hurry to avoid any further destruction.
End of book 3