Tris finds herself in a world outside of her old one, which turns out to be an experiment and finds herself in a whirlwind romance with Tobias and learning about this new place, the fringe and the purity war. Then it's discovered that long ago the government messed with genes and some are known as GP (geneticaly pure, no messed up genes) or GD (geneticaly damaged, messed up genes) and GD's are looked down upon. The Divergent are GP's and, after an examination, Tobias and Tris discover Tris is GP and Tobias is not. Also Marcus is sentanced to go outside, where Tobias finally escaped him. Then a girl named Nita draws in Tobias to a revolution, one Tris dosen't trust. Tobias continues to help and participates in a explosion that puts Uriah into a coma he'll never wake up from. They almost break up but get back together and lead a real rebellion, one that Tris sacrifices her life for for the greater good. Overcome with grief, Tobias nearly erases all his memories, stopped by Christina, a close friend of Tris. They later become good friends themselves. You will feel the love for the couple as they discover the other is a part of themselves and will be teared apart like Tobias when Tris is gone. An amazing ending to an incredible series.