Uglies 

In Tally's world, your 16th birthday brings an operation that turns you from a repellant Ugly into a stunningly attractive Pretty, and catapults you into a high-tech paradise where your only job is having a really good time. Just before her birthday, Tally discovered that turning Pretty comes with a terrible price. She vowed to accept the operation, but with the understanding that her friends on the outside would rescue her, and let her be the guinea pig for the experimental and highly dangerous cure they're developing. But in the second book of the Uglies series, Tally's Pretty. And everything's changed. The new, Pretty Tally is totally happy right where she is. She doesn't think she needs any kind of cure at all. When someone from her Ugly life shows up with a message, Tally has a hard time listening. Did she really promise to give all this up? Is she bound by a promise she made when she was a different person? If there is anything left of the old Tally, how will she fight her way out to keep her word and help her friends? - from Amzon