Allegiant recap

After the city's founding secret is revealed, it fractures under Evelyn's harsh factionless rule, and a group loyal to the old factions, the Allegiant, forms to obey the message urging people to go outside. Tris, Tobias, Caleb, Christina, Peter, and others escape beyond the wall and reach the Bureau of Genetic Welfare, where they learn the truth: long ago, attempts to genetically engineer away human flaws produced people deemed genetically damaged, and the walled cities are experiments meant to restore genetically pure humans over generations. Divergents are the genetically healed. Tris is judged genetically pure while Tobias is called damaged, which shakes him. When the Bureau prepares to wipe the memories of everyone in the rebelling city with a serum, Tris and her friends resolve to turn that serum on the Bureau instead. Caleb volunteers for the deadly mission, but Tris takes his place, survives the death serum, and releases the memory serum, only to be shot and killed by David. Tobias, devastated, helps broker peace in the city, and after Uriah dies of his injuries, the survivors slowly rebuild. Years later, Tobias scatters Tris's ashes over the city she helped free.

Previously, across Divergent and Insurgent: in a walled city sorted into five virtue-based factions, Beatrice Prior discovered she was Divergent and left Abnegation to join Dauntless as Tris, falling in love with her instructor Tobias, known as Four. She helped stop the Erudite leader Jeanine Matthews, who used a mind-control serum to turn Dauntless against Abnegation, losing her parents and being forced to kill her friend Will. In the turmoil that followed, the factions collapsed. The factionless, led by Tobias's presumed-dead mother Evelyn, rose to power, and the uprising ended with Jeanine's death and the seizure of a hidden message. That recording, from an ancestor named Edith Prior, revealed that the city is a controlled experiment and that its people are meant to leave the walls for a wider world once enough Divergents emerge, shattering everything the survivors believed about their world.

The revelation throws the city into turmoil. Evelyn and her factionless rule harshly, confiscating weapons and crushing opposition, while a group loyal to the old factions and to Edith Prior's message, the Allegiant, forms under Johanna Reyes to defy her and go outside. Tris, Tobias, Caleb, Christina, Peter, Uriah, and others decide they must see the truth of the world beyond the wall for themselves. Slipping past the factionless, the small group escapes the city and crosses into the unknown land outside, uncertain what they will find and leaving a fracturing city behind them.

Beyond the wall the travelers reach the Bureau of Genetic Welfare, a government compound that has watched their city for generations. There they learn the truth behind the experiment: long ago, efforts to genetically engineer away human flaws created people labeled genetically damaged, and the walled cities were established to breed and restore genetically pure humans over time. Divergents are the genetically healed the project sought. Tris is judged genetically pure while Tobias is called damaged, a distinction that wounds him and tests their bond. As they navigate the Bureau's politics under its director, David, word arrives that Evelyn's grip on the city is tightening toward open war.

Learning that the Bureau means to quell the city's uprising by wiping everyone's memories with a serum, Tris and her friends resolve to turn that serum on the Bureau instead. The mission requires braving a Weapons Lab guarded by a lethal death serum; Caleb volunteers to atone for betraying Tris, but she takes his place at the last moment. Tris survives the death serum and releases the memory serum, but David shoots her before it takes effect, and she dies. Tobias, devastated, helps stop all-out war in the city and persuades Evelyn to relinquish power, easing the conflict, while Uriah dies of earlier injuries. In an epilogue years later, the survivors have begun to rebuild a freer world, and Tobias scatters Tris's ashes over the city she gave her life to save.

The Bureau of Genetic Welfare decides to end the uprising in the city by releasing a serum that will erase everyone's memories, including those of Tobias's family and friends. Tris and her group resolve to stop it by turning the memory serum on the Bureau's own staff instead. The plan requires someone to enter a heavily guarded Weapons Lab protected by a lethal death serum. Caleb, seeking to atone for betraying Tris, volunteers for what is meant to be a suicide mission, but at the last moment Tris takes his place. She endures the death serum and succeeds in releasing the memory serum, resetting the Bureau, but David, the Bureau's director, shoots her before it can take him. Tris dies. Tobias, shattered by grief, works to prevent all-out war in the city and helps bring Evelyn to give up her hold on power, easing the conflict between the factionless and the Allegiant. Uriah, gravely injured earlier, dies of his wounds. In an epilogue set more than two years later, the survivors have begun to rebuild a freer life, and Tobias scatters Tris's ashes by zip-lining over the city, honoring her.