The Divergent Series: Allegiant is part of something.
Allegiant (novel) . It completes the Divergent trilogy that Roth started with her debut novel Divergent in 2011 . The book is written from the perspective of both Beatrice ( Tris ) and Tobias ( Four ) . Allegiant was published simultaneously by Katherine Tegen Books and HarperCollins Children 's Books in the U.K. Four weeks earlier , a free electronic companion book to the trilogy titled The World of Divergent : The Path to Allegiant was released online . The Divergent Series . They acquired film rights to the Allegiant novel in December 2013 , deciding in April 2014 to split the third novel into a two-part film adaptation . The Divergent Series: Allegiant . It is the first of two cinematic parts based on the novel Allegiant , the final book in the Divergent trilogy by Veronica Roth , and the third installment in The Divergent Series .