This is a difference, rather than something that's missing, but it's a pretty big change. In the first book, Kate Winslet's character Jeanine Matthews has a much smaller role. In the movie, she gives the spiel at the Choosing Ceremony, and she's leading the charge when the Dauntless members are being controlled. That whole final sequence with the showdown with Tris, the truth serum, and getting her hand stabbed? All new for the movie.