In this closing volume of the trilogy, Katniss is prevailed upon to be the propaganda queen of the rebellion, which irks her. The by now rather bloodthirsty Katniss wants to fight, but she agrees to be a figurehead on condition that all the surviving Hunger Games victors are granted immunity and she herself is granted the sole right to kill President Snow.
She's relegated to the task of being a pretty face in films, but what she did not count on is Peeta appearing as the propaganda king for President Snow, even though it's obvious he has been brainwashed. He compatriots realize that this burden of what has happened to Peeta is hampering her effectiveness, so they organize a rescue upon which she is not allowed to go. The rescue is successful, but the brainwashing is deeper than anyone imagined. Peeta really does believe the propaganda he was spewing, and he tries to kill Katniss when they meet. This part was included as the finale to the second volume in the movie series.
They set Peeta on a long, slow, painful road to recovery, and in time, he becomes well enough to join them in the fight against the capital. Eventually, Katniss also takes up a weapon and begins to fight, becoming one of the important assault teams on the capital after a propaganda shoot in what was supposed to be a safe part of the capital goes completely south.
They set themselves the mission of hunting down and killing the president. Katniss's team is heavily mauled, losing soldier after soldier. Katniss becomes separated and finds herself on her own as she closes in on the president's residence, which is now housing children in the hope that it will prevent the rebels from bombing it. She espies a hover plane with capital markings dropping supplies to the children, but the parachutes explode, killing scores of them, including Katniss's young sister Prim.
This is more than Katniss's over-stressed and weakening psyche can take. The victorious President Coin, of the rebel army, orders a Hunger games using the capital's children. While waiting to take up her role of executioner in the public display of President Snow's capital punishment, Katniss encounters Snow by accident awaiting her killing him. He informs her that he did not order the parachute bombing of the children. He reminds her that he and she agreed some time ago never to lie to one another, and his explanation that if he'd had access to a hover plane he would have used it to escape (but we’re never told to where!), and that he had no reason to assassinate children and turn everyone against him rings true to Katniss. Snow indicates that the bombing was Coin's idea.
Katniss remembers that her longtime friend Gale had once arranged a trap which is disturbingly reminiscent of the attack on the children but when she confronts him, he denies responsibility. At the execution, Katniss spares Snow and shoots her arrow into Coin, instead, killing her. There is chaos after this, during which Snow himself is killed. Katniss is tried for the murder of president Coin but is acquitted by reason of insanity and is sent home to district 12 where she eventually takes up residence with Peeta, not too far away from Abernathy's home. The three of them write a book honoring the combatants in the Hunger games and the ensuing war.
As time passes and the raw edges ease, Katniss and Peeta have children and life assumes a vague semblance of normality, but Katniss dreads the day when she will have to tell her children the truth about what she did in the games and in the war.