Allegiant is the 3rd (and final) book in the Divergent trilogy written by Veronica Roth. Tris and Four find themselves in the middle of a deeper conspiracy than even they could imagine and it changes everything they once thought was right and true.
Without giving too much away, Roth changes the voice of how the Divergent story is told in Allegiant. Prior to this, the story is told through the eyes and perspective of Tris. We hear her voice and process the events with her.
For Allegiant, Roth uses both Tris and Four as the narrators. This takes a bit of getting used to as each chapter, the perspective changes. Can’t tell you how many times I had to reread the beginning few paragraphs of a chapter because it was a bit confusing.