Pandemonium by Lauren Oliver is a novel about a futuristic society that attempts to cure the people of love by forcing people to endure a medical procedure that prevents them from feeling. In this world, cleanliness is Godliness and everyone holds the same beliefs, feels the same non-feeling, and roles are performed dutifully with little feeling. One's duty to country comes above one's loyalty to family. Spouses are matched by the government and children are born out of a contract with the government. This creates a clean and sterile world, with no people who aren't "perfect."

The novel begins with Lena who has just entered a new high school. The first chapter is elusive but the reader knows that Lena is different and that she possesses a knowledge that the other high school students don't have. From this point the novel begins alternating between the Now thread and the Then thread.

In the Now: Lena has begun attending a new high school. Throughout these sections there are brief flashbacks of what Lena's life used to be like. She used to believe what all of the others believed, that the DFA was an organization that protected people and that everyone must have the procedure for society to go on. In the Now, Lena is working covertly with Raven and Tack, two of her friends in the resistance. She goes to a rally where Julian Fineman, the DFA organizer's son, is present. He is kidnapped and it is her job to stay with him no matter what.

She finds Julian in an underground subway tunnel that has long been abandoned. They are captured by what they think are Scavengers — a rogue group that helps neither the DFA nor the resistance — but in reality they have been captured by the DFA. Julian and Lena escape and Lena is brought back to Tack and Raven, but Julian is scheduled to be executed as a punishment for falling in love with Lena.

In the Then thread: Lena escapes from her neighborhood with a boy named Alex. Alex is killed as they cross the border and Lena wakes up in the Wilds being taken care of by Invalids. Raven, Blu, and Lu nurse her back to health. She lives with them for some time on the Homestead. Life on the Homestead is difficult and rudimentary. Food is scarce and the people are constantly on the lookout for attacks. As the group is preparing to move south for the winter months, they are attacked. They flee, regroup and head south with little food or supplies. Again, they are attacked at a southern homestead and Lena, Raven and Tack assume fake procedure marks and enter the regular world as part of the resistance.

It is at this point in the novel where the Now and Then threads converge in Chapter 13.