This entire trilogy was the story of the two leads, and the people around them. About how these two people got the people they cared about into the very settings to begin with, about how they survived, escaped it and went around trying to save themselves. How the girl remembered things along the way. How she sacrificed everything she had, and went the other path to find a cure because she believed so greatly she can find the cure. How it cost her the trust of the people she cared about, especially the boy she loved the most. How the absence torn them both. How she eventually did it, found the cure, save the boy she love and the world. But didn't get to live to see it. She sacrificed everything she had because she believed in something bigger so strongly, and that was saving the world. She 'turn her back on her friends' because she didn't want to turn her back on the world. And her death comes with a great absence and hollow in his heart. And through him she will continue living.