Divergent - Veronica Roth
The 4 books series happens in a post-apocalyptic Chicago, where the society is divided between 5 factions: Abnegation, Amity, Candor, Dauntless and Erudite. Each year, all the 16-year-old kids have to choose a faction to live in. Before the choosing, they have to be tested. The test shows them which faction they fit the most, based on their characteristics: Abnegation for the selfless, Amity for the peaceful, Dauntless for the braves, and Erudite for the intellectual. Beatrice Prior is a 16-year-old girl that was born in Abnegation. She never thought that she is fitted to the faction. Before the choosing, she gets her test results, that were very unusual: she fits to 3 factions. She is divergent.
With this information, she chooses the Dauntless faction. At the beginning of the hard training, she meets her mysterious trainer, with a strange name: "four". During the training, she is exposed to many secrets that, one after another, reveal the great cover of lies that filled the city.