After being captured and surgically transformed into a "special," teenaged Tally Youngblood, now a government agent programmed to protect society from outside threats, is ordered to eliminate the rebel colony New Smoke, Tally's former home.

Tally's perfect life as a Pretty is disrupted when she receives a letter from herself, written when she was an Ugly, reminding her of the promise she made to take a drug developed to cure the brain lesions that keep the Pretties shallow and happy--and when she takes the pills, she becomes a target of those determined to keep Pretty society carefree.