Shay and Tally are getting ready for a costume party in New Pretty Town. Tally's recently turned pretty and she is about become a Crim, which is a special group of pretties who spend their time doing rebellious things. At the party, Tally notices that she is being watched by a figure in a Special Circumstances costume.
Tally meets the leader of the Crims Zane. The figure watching Tally is one of her previous friends from the New Smoke and he tells her that he has a package for her which he will leave in Valentino 317 for her to pick up. Tally feels her head finally clear from all the excitement, she is bubbly, and starts to remember her life before turning pretty.
The next day Tally has a date with Zane and the two talk about being bubbly and what makes their thoughts become clear. They learn that one of the things includes kissing and Tally tells Zane about Croy from the previous night and what he told her. The two decide to go to Valentino mansion to find a room 317 and see what Croy left for Tally. When they arrive there, they realize that the room 317 is hidden on the roof of the building. The key to the room is hidden at the tower so they have to climb to get it which is being broadcasted all over New Pretty Town, but Tally and Zane don't know it yet.
When they enter the room 317 they discover the package left for Tally. It contains two pills and a letter. The letter is written for Tally by Tally, when she was still ugly and about to surrender herself to become pretty. The pills are a cure for her pretty-mindedness, Tally explains in the letter about the lesions that are put inside her head during the operation to make her forget her former self. They hear the wardens approaching them and Tally and Zane decide to share the two pills, one for each.
It is clear from the start that the operation made Tally forget almost everything about her former life. The thing that she remembers are made to look stupid and childish, a trait of her ugly self. The way that she talks and the fact that her only worry is about the clothes she is going to wear shows that she is completely changed.
The language the pretties use is distinctive; words and phrases like bogus, pretty-making etc. show how simplified their thoughts and their view of the world actually are.
Tally and Zane are wearing prison cuffs on their wrists that track their conversations and where they move. Their adventure to the room 317 made them famous among the Crims. The two and the rest of the Crims are planning to melt the ice of the skating court that stands above a stadium. Their plan works and everyone on the ice falls down to the stadium. The experience makes all of the Crims present there bubbly for a long time. Being bubbly is opposite of being pretty-minded.
On the night of their celebration Zane gets a strong headache caused by the pill and he goes to his room. Dr. Cable approaches Tally and asks her to join the Special Circumstances. Tally, of course, refuses. Shay approaches Tally after that and confronts her about their past from the Smoke; the bubbly experience made Shay remember everything. Tally tells Shay about the pills and the cure. Shay is angry at Tally for not sharing the pills with her and breaks off their friendship.
Tally, Zane and Fausto, one of their Crim friends, meet with a couple of uglies who helped Tally before she turned pretty. They say that they have evidence that the New Smoke is still functioning. They also share that they've seen some Crims secretly visiting one of the parks in New Pretty Town and behaving strange. Tally asks them to lead the way to there. They arrive to a disturbing sight. Shay and a few other Crims are performing a ritual where they cut their arms to draw their blood. Tally realizes this is their way of staying bubbly, this is Shay's cure.
Zane suddenly starts to have hard time breathing and Tally rushes him to hospital. When they get there he is feeling better, but has to give the doctors a reason they rushed there, other than an attack caused by the cure, so Zane breaks his arm. One of the doctors starts asking Tally questions about Shay and the recent events.
Zane and Tally realize they have to leave the New Pretty Town soon and find the New Smoke to help Zane because the side effects of the cure are getting worse. For the next days they plan their escape along with trying to figure out how to take the prison cuffs off. Tally finally gets an idea to use hot air balloons to escape and to use the fire to break the cuffs. All of the Crims are in on the plan as well. The plan works and the Crims are out of the town. The next step is to jump off the balloons and get onto their hover boards to escape further. All of the Crims jump. Tally and Peris are last. Peris chickens out and wants to go back. He holds Tally back trying to make her change her mind as well. This results in Tally losing the ground that will make the hover board catch her. Hopeless, she starts to think about what will happen to her now that she is going to be captured until she sees a river. She takes the opportunity and jumps.
The cure worked, aside from Zane's headaches, which are getting worse day by day. Shay feels betrayed by her friend and takes a dark path which will only get darker. The New Pretty Town is faced with the biggest rebellion yet and Tally is the face of it.
In the final scene where she is faced with the disappointment cause by her best childhood friend is a turning point in Tally's determination to not be a pretty any longer, to let go of her past and jump forward.
Tally crashes into river but loses her hover board. She begins walking towards the appointed meeting place of the Crims after the escape. Tally realizes it's going to be a long walk through the wilderness. On one of the nights she wakes up to a sound of screaming and realizes she is being hunted by a group of odd-looking men. They capture her, but when they see her face their approach changes and they start treating her like a god. The hunters take her to their camp and there she meets a man called Andrew who tells her that he is a god's man. He is seen as a prophet of the camp that talks to gods.
The next day Tally convinces Andrew to take her to "the edge of the world". It turns out to be an electrically charged border and anyone who tries to go past it starts to tremble and lose control of their body. Tally realizes that she is in a reservation with no way out on the ground. Andrew tells her that the place is often visited by doctors, which are anthropologists, via hover cars. Tally decided to wait for their visit and steal their hover car. She learns that the reservation is used for human testing; they test the human nature and how it can be manipulated meaning that the experiment of turning pretty started here. She tells Andrew that they are both just humans and that his world is used for manipulation to which Andrew replies that he knows. Determined to return to this place and help these people Tally escapes with the hover car.
Tally arrives to the Ruins and, to be safe, walks to the meeting place in hopes that there is still someone there waiting for her. Someone is indeed there; it is David. Seeing David after so much time and all of the changes, feels strange to Tally. David takes her to the New Smoke. She discovers that Zane is in bad condition due to the cure. He barely got to the meeting place before he collapsed. His condition is stable now but he may face permanent damage. David's mother tells her that the pills where made to be taken together. Zane took the pill that destroys the lesions and Tally took the pill that repairs the damage made by the first pill. That's why Zane's brain got damaged but the pill Tally took was useless, it had no effect. This means that Tally cured herself without the cure.
Tally goes to take a bath but suddenly David runs up to her checking if she has a tracker. Someone has a tracker which revealed their location to the Special Circumstances and they are on their way so the New Smoke has to pack up and leave. Tally realizes that the tracker is in Zane, in his tooth. Doctors at the New Pretty Town put the tracker there while he was unconscious at the hospital. Maddy, David's mother, is unable to remove the device from him meaning they have to leave Zane behind. Tally refuses to leave him, even though David begs her to come with him.
The Special Circumstances arrive with an unpleasant surprise. Shay is now a part of them, she is a special. Her appearance has drastically changed; she has a monstrous look to her. She tells Tally that she will become special as well.
The hunters' camp and their entire system of life and the fact that the entire reservation is made as an experiment is a cruel and surprising twist of the plot. These people represent the pre-civilization, their lives based on instinct and seemingly pointless circle of blood revenge; they are intentionally kept out of the civilization and knowledge so that they can be easily manipulated which adds a new element of cruelty to the entire system of artificial humanity.
The second book ends similarly to the first one: Shay has gone through a drastic change and Tally is once again forced to go through the same.