Paper Towns 1

I think that when Margo came up to Quentin's window and got him to come with her and help her out with her mission of revenge. This definitely changed Q's personality, and you could tell, not only because of all of the things he and Margo did that night, but also what happened the next day, and throughout the rest of the book. He stood up to some of the bullies, like Jase, and Chuck, and then stood up to himself, and his friends, in order to find Margo.