The third and final novel in the Hunger Games trilogy opens with Katniss Everdeen walking through the remains of District 12, her former home. She is filled with guilt for her role in inciting the uprising and anger against President Snow for his oppressive tactics. Meanwhile, Peeta Mellark has been captured by the Capitol. After her dramatic rescue from the Quarter Quell arena, Katniss has been living in District 13 - the District all of Panem thought had been decimated, but was actually home to the Capitol's secret nuclear development program. Later, District 13 leveraged the nuclear arsenal to threaten the Capitol and gain autonomy. It is now where the rebellion is headquartered.
Katniss, Gale, her mother, and Prim all live in District 13's vast underground community and abide by President Coin's militant systems. Katniss does not quite trust Coin yet, especially since District 13 stood by and watched all the other districts suffer at the hands of the Capitol for years. However, Coin needs Katniss, the Mockingjay, to be the symbol of the rebellion and rally the other Districts' support. Katniss only agrees to the role if Coin will acquiesce to her demands. Coin publicly accepts Katniss's conditions and retaliates with one of her own: if Katniss deviates from the prescribed mission, "it will be viewed as a break in the agreement" (58).
Katniss's first duty as Mockingjay is to film "propos" - televised calls for resistance. Fulvia Cardew tries to put Katniss on a stage to perform scripted lines, but she fails so badly that it makes Haymitch laugh. Everyone soon agrees that Katniss is at her best when she is natural. In District 8, Katniss and Gale visit a makeshift hospital and meet Commander Paylor. Katniss's production team (Cressida, Messalla, Castor, and Pollux) film her meeting the patients. Katniss's presence inspires them to keep going. While Katniss is there, the Capitol attacks District 8, including the hospital. Katniss, riled up, is performs passionately for the camera, announcing to the Capitol: "IF WE BURN, YOU BURN WITH US!"
As a result of Katniss's statement, the Capitol televises Peeta begging her to call for a ceasefire. During the broadcast, he alerts District 13 of an imminent attack and is severely beaten. However, his warning helps the rebels quickly call for a lockdown, weathering the three-day attack without any casualties. Katniss feels so guilty about Peeta's circumstances that she can no longer fulfill her duties as Mockingjay. After the lockdown is lifted, the rebels decide to mount a mission to rescue Peeta (and Annie). Meanwhile, Katniss and Finnick film new propos in which Finnick reveals all the secrets he knows about prominent Capitol citizens.
The rescue is successful and Peeta, Annie Cresta, and Johanna Mason all return to District 13. Katniss is overjoyed to see Peeta, but his first reaction to her presence is an attempt to strangle her. She finds out that the Capitol has "hijacked" Peeta; he is now programmed to think that Katniss is his mortal enemy. Meanwhile, Katniss is needed in District Two, which is the only holdout in the uprising. In order to gain control over 2, the rebels must crack "the Nut," the mountain in which the Capitol keeps all its weaponry. Gale comes up with the ruthless idea to create avalanches - which would disarm the Capitol but also trap all the innocent District 2 miners inside.
Katniss voices her dissent but President Coin supports Gale's plan, and it succeeds. Katniss, though shaken, must use this opportunity to demand the Capitol step down since it's clear they are losing ground. However, while she is filming, two trains full of survivors come careening out of the Nut, many of them armed. The battle starts anew, but Katniss can't take it anymore. She tries to negotiate with the District 2 survivors and is shot in the process.
Back in District 13, Peeta has become calmer but still addresses Katniss in a nasty tone. For the first time, loyal Peeta can see Katniss's flaws, and she does not like it one bit. Meanwhile, Finnick and Annie get married. After the rebels have had time to regroup, they start to prepare for the final battle: taking down the Capitol. Katniss is assigned to Squad 451 (a group of Sharpshooters led by Boggs).
Katniss and Gale are disappointed to find out that Squad 451 will be the "Star Squad," or the public face of the rebellion. This means that they will not be active in battle. They do not have a choice but to fight, though, when a "pod" kills Soldier Leeg 2. Coin quickly sends a replacement: Peeta (who still is wired to kill Katniss). Suddenly, Katniss realizes that Coin wants her dead. The Star Squad faces tragedy again while filming a complex fake battle sequence - Boggs triggers a pod that blows off his legs. Another pod unleashes a wave of toxic black gel, and yet another kills Soldier Mitchell. Before Boggs dies, he transfers his Holo (like a GPS of the Capitol that points out the pods) to Katniss and tells her not to go back to District 13.
Squad 451 moves forward through the Capitol with Katniss in the lead. A televised Capitol broadcast proclaims that the members of Squad 451 are dead. After watching himself nearly kill Katniss on television, Peeta decides that he should die, and only Katniss can talk him into continuing. Pollux leads them into the maintenance shafts below the Capitol. But Snow is one step ahead of them and as they find themselves getting closer to his mansion, he unleashes a pack of wild reptilian mutts. Only Pollux, Gale, Cressida, Peeta, and Katniss manage to escape alive. Cressida leads them into a grimy store selling fur underwear run by Tigris, a former Hunger Games stylist and rebellion sympathizer. Tigris offers Squad 451 refuge in her hidden basement.
The next day, most of the Capitol citizens have been evacuated. Upon hearing that the more fortunate Capitol homes (even President Snow's) are taking in refugees, Katniss decides to refocus on her mission to kill Snow. Tigris disguises the rebels and they take off - Cressida and Pollux are the guides, Katniss and Gale are the refugees looking for shelter, and Peeta is there to create a distraction if needed. They are quickly separated and Katniss reaches Snow's mansion alone. She sees Capitol children gathered on his lawn - a human shield for Snow. Then, a Capitol hovercraft appears above the children and drops bombs on them. Just as the rebel medics (including Prim) rush in to help, the bombs explode again. Prim is killed and Katniss is badly burned.
When Katniss awakens in a Capitol hospital, the rebels have won the war and Coin rules over Panem. When wandering around the President's mansion in a daze, Katniss comes upon the fallen President Snow, chained and dying in a a room full of roses. He tells her that Coin orchestrated the attack that killed Prim. While Katniss and Snow were focused on destroying each other, Coin managed to manipulate them both and take over Panem without compromising District 13. Katniss takes some time to deal with this news, but Snow's assertions are solidified when Coin suggests holding a Hunger Games with Capitol children. During the victory ceremony, Katniss fires her ceremonial arrow into Coin, even though Snow is standing right next to her.
Katniss is drugged and held in the mansion for weeks until Haymitch comes to fetch her. He tells her that her trial is over - Plutarch and Dr. Aurelius argued that Katniss acted out of insanity, securing her freedom. She's now free to go home to District 12. Commander Paylor is now president. Back in District 12, Katniss struggles to put herself back together. Gale gets a fancy job in District 2, and Katniss's mother is starting a hospital in District 4. Soon, Peeta returns to District 12 and he and Katniss grow back together.
In the epilogue, Katniss shares that she ended up with Peeta because she needed his faith and loyalty more than Gale's inner fire (since she has enough of her own). 20 years later, they have children - a girl and a boy. Even though Katniss and Peeta are still haunted by their Hunger Games experiences, they are moving on - together.