The official trailer for "Allegiant," the third installment of "The Divergent Series" reveals a major plot twist and a new purpose for main character heroine Tris Prior (played by Shailene Woodley). She must scale the walls to see what's beyond the realm of post-apocalyptic Chicago to save the world, MTV reported. .

The film franchise is based on of the book trilogy by author Veronica Roth and takes place at some point in the future, although the exact year is not revealed. The city of Chicago is divided into four factions of people based on a personality trait, according to MTV.

But it is revealed that there is a fifth faction called the Divergents, full of people who possess multiple personality traits. Prior finds out she's part of the Divergent faction, which means she's a threat to the system because she is the key to unlock a bigger secret.

Prior finds out that there is more beyond the walls of the post-apocalyptic Chicago and literally scales the wall to find out what's behind them in a scene in a trailer. Once she reaches the top, Prior is greeted with a vast view of reddened skies and ruins.

The trailer also gives fans a sneak peek into new character David, played by Jeff Daniels who was recently cast in the new key role, according to the Hollywood Reporter.

"Tris it is a pleasure to finally meet you," David tells Prior. "You saved the city, help me save the world."

The third book in the "Divergent" trilogy will be split into two parts, "Allegiant" and "Ascendant," according to Entertainment Weekly. "Allegiant" is scheduled for a March 18 release.

Watch the trailer below.