Allegiant Shailene Woodley, Theo James, Jeff Daniels. Directed by Robert Schwentke. Rated PG-13. Opens Friday citywide.

At the end of last year’s Insurgent, the second movie based on Veronica Roth’s Divergent series of YA science-fiction novels, it seemed like the story of Tris Prior (Shailene Woodley) and her battle against her rigidly segregated dystopian future society had essentially wrapped up. She had destroyed the hierarchical “faction” system of dividing people by personality traits, and defeated the power-hungry bureaucrat who ran it all. She had made contact with the outside world and discovered a society that existed beyond her own, giving her peers a chance to escape their walled city.

The series’ third installment, Allegiant, loosely adapted from parts of Roth’s final novel, throws in a ton of new plot elements to justify continuing the story, but it never succeeds. With the factions destroyed, the world of the series turns into your basic post-apocalyptic landscape, complete with an irradiated wasteland and a small elite enclave of survivors who secretly control the world. With one evil bureaucrat dead, Tris and her friends simply move on to the next, a blandly sinister scientist played by Jeff Daniels, who’s no match for Kate Winslet’s villainy in the other movies.

The plot of Allegiant is so convoluted and yet so inert that it feels like the screenwriters are making it up as they go along, constantly inventing new terms for various groupings of characters. Tris, who heroically liberated her society over the course of the first two movies, ends up with almost nothing to do, a pawn in the ill-defined plans of leaders played by Daniels, Naomi Watts and Octavia Spencer. Her romance with boring hunk Four (Theo James) is reduced to a handful of kisses and clutches doled out over the two-hour running time.

Woodley remains a solid actor, but she’s defeated by the incoherent script and the surprisingly terrible special effects, which turn a number of ostensibly tense moments into inadvertent comedy. Veteran actors Daniels, Watts and Spencer don’t fare much better, and Daniels has one exclamation of “Nooooo!” that might mark the low point of his entire acting career.

By the time it wraps up, Allegiant leaves the characters in practically the same place they started, with no immediate threats other than an uncertain future. Director Robert Schwentke is stepping down for forthcoming final installment Ascendant, but it’s hard to imagine anyone pulling a satisfying or cohesive finale out of this mess.