A few months after winning the 74th Annual Hunger Games with Peeta Mellark, Katniss Everdeen, now 17, is adjusting to her new life of plenty after spending her entire childhood in poverty and hunger. Despite her family's lush new house in Victors' Village and the newfound wealth, Katniss still hunts in order to feed her friends. Her hunting partner and best friend Gale Hawthorne now works in the coalmines. They shared a single kiss, but she’s confused about their relationship.
President Snow pays Katniss a visit, threatening her loved ones if she doesn’t convince Panem that her final act in the Games – pulling out poisonous berries to kill herself and Peeta – was motivated by love and not defiance. She does her best to keep up appearances on the Victory Tour, but understands she may have to resort to marrying Peeta or run away. When they stop for a celebration in District 11, an old man whistles Rue’s four-note mockingjay tune and the citizens offer their thanks to Katniss. The man is killed by Peacekeepers. Trouble is brewing in the districts, and Katniss is stroking the flames, whether she means to or not.
Peeta proposes to Katniss on live TV, but President Snow is still not convinced it’s enough. Back home, Katniss sees a transmission intended for Mayor Undersee and learns that District 8 has revolted. She tries to convince Gale to run away with her, but he knows the time is ripe for rebellion. Katniss approaches Peeta, who agrees to flee. However, they see Gale being whipped in the square by Romulus Thread, the brutal new Head Peacekeeper. Katniss gets in between Gale and the whip and Thead relents in his assault against her only when Haymitch intervenes. She takes Gale to her mother's house, where she tries her best to heal his wounds. That night, Katniss sits up with Gale and kisses him, realizing how much she loves him.
Over the next few days, District 12 becomes a police state. Armed guards are everywhere, crimes tolerated for years are suddenly to be punished to the full extent of the law, and the Hob is burned down. The mines are shut down for 2 weeks, bringing the District to the brink of starvation.
Katniss finds Bonnie and Twill, escapees from District 8, in the woods. They tell Katniss they are heading to District 13. Katniss is confused - District 13 was bombed 75 years ago in the Dark Days of the war with the Capitol. Twill tells her that each time a clip of 13's burned-out Justice Building is broadcast, a mockingjay flies through the shot in the upper right-hand corner. It has to be the same footage used over and over again. Twill thinks the survivors have survived underground and that the Capitol leaves them alone because of their chief industry before the war - nuclear development. Recuperating from injuries sustained getting over the newly electrified fence, Katniss sees two reports about District 13 that confirm Twill’s story about the mockingjay. Haymitch is skeptical about this information. Despite rumors of uprisings in Districts 3, 4, 7, 8 and 11, he tells Katniss an uprising in 12 is impossible.
Katniss and her family watch the "reading of the card," the announcement of the rules for the Quarter Quell, the 75th annual Hunger Games. This year, the tributes from each District will be chosen from the pool of existing victors. As the only female victor in District 12, Katniss must return to the arena.
Katniss approaches Haymitch and they agree they owe it to Peeta to keep him alive no matter what. The three train like Careers and review footage of previous victors. As expected, Peeta volunteers for Haymitch and he and Katniss head to the Capitol again - this time without getting to say goodbye to their families.
At the Opening Ceremony, Cinna dresses Katniss in a jumpsuit that glows like an ember. She is still the girl on fire. They meet some of the other victors - flirty Finnick Odair from District 4, Haymitch’s friend Chaff and Seeder from 11 and contemptuous Johanna Mason from 7. Haymitch advises Katniss and Peeta find allies among the victors. Katniss is drawn to Wiress and Beetee, smart, odd victors from District 8 and 80-year old volunteer Mags from 4.
Cinna dresses Katniss in her wedding dress for her interview and when she twirls at his command, the dress burns away to reveal one that makes her look like a mockingjay. Peeta's interview is similarly shocking; he tells the audience he and Katniss already married in secret and that she is now pregnant. Haymitch tells them both to stay alive, but also reminds Katniss to remember who the real enemy is. Before she launches into the arena, she is trapped in her tube, forced to watch Cinna beaten and arrested.
In the arena, water spreads out in every direction, surrounding a little island that houses the Cornucopia. 12 spokes of land radiate from the island. In concentric circles from the island are sections of saltwater, beach, then jungle. The pink sky is a force field dome surrounding the arena. Katniss swims for the Cornucopia and makes the quick decision to team up with Finnick; noting that he wears a gold bangle like the one Haymitch wears. They arm themselves and take Peeta and Mags, who hops on Finnick's back, into the jungle. As they climb, Katniss can't warn Peeta in time and he runs into a force field. Electrocuted, his heart stops but Finnick revives him. They press on in search of water, eventually camping at nightfall. From the nightly broadcast, they learn eight tributes have died, including Seeder. A sponsor gift arrives - a spile (spigot) for collecting the water that runs inside the trees. Later, twelve bells toll and a lightning storm begins a distance away. An hour later, rain falls nearby. An hour after that, a poisonous fog appears on the ground. Katniss wakes her friends and they run, but the chemical fog damages their nerves. Finnick takes Mags and Katniss helps Peeta but they soon have to swap. Katniss falls and Mags sacrifices herself by walking into the fog. Before it kills them, the fog is vacuumed up and out of the arena.
Katniss, Peeta and Finnick crawl to the beach. The salt water leaches the poison out of them. A swarm of orange monkeys appear in the jungle and Katniss realizes they are about to attack. Katniss, Finnick and Peeta defend themselves and the morphling girl from District 6 jumps in front of a monkey set on tearing into Peeta. Her wounds are fatal, and Peeta soothes her as she dies. The next day, they join up with Johanna, Beetee and Wiress, who keeps repeating the phrase "Tick, tock."
At what Katniss assumes is noon, the same tree that was struck by lighting the night before is hit again. Katniss remembers that the twelve bongs that preceded the first bolt and it hits her - the arena is a clock. The tree is in the first "wedge" of jungle created by the spokes of land radiating from the Cornucopia island. 12 o'clock. Each wedge corresponds to an hour of the day when a particular hazard occurs in its section. Lightning in the first clockwise wedge between 12 and 1 starting at midnight, blood rain from 1 to 2, fog in 2 to 3, etc.
At the Cornucopia, the group of allies are ambushed by the Careers. Wiress is killed and the allies kill Cashmere and Gloss. Finnick deflects a spear aimed at Peeta. Later, Katniss thinks about the events so far - Finnick retrieving Peeta from his plate in the water, Finnick reviving Peeta, the morphling saving him from the monkey attack, and Finnick blocking Brutus's spear. Like Katniss, the other tributes are protecting Peeta.
Jabberjays mimicking Prim and Finnick's love Annie Cresta disturb them. By nightfall, two-thirds of the tributes have died in the first 36 hours of the Games. Peeta and Katniss take watch and they come clean with one another - each is trying to save the other. Peeta insists that Katniss has more to live for. But Katniss wants to make the world safe for Peeta's child. He must live.
Beetee comes up with a plan to use his wire to electrify the beach and water in order to kill Brutus and Enobaria. The wire must be threaded through the jungle from the lightning tree. While examining the tree, Katniss finds a weak spot in the force field beyond the tree. At 9 o'clock, Beetee weaves the wire around the trunk. He instructs Johanna and Katniss to lay the wire down through the jungle from the tree to the beach. Katniss kisses Peeta goodbye. As she and Johanna work, the wire is cut from above them. Johanna jumps onto Katniss and stabs her left arm, then runs off when Brutus and Enobaria arrive. Thinking their alliance is severed, Katniss races to Peeta. She finds Beetee unconscious by the tree, a knife wrapped in wire beside him; the wire leading to the tree. As Katniss plots to take out as many tributes as she can to leave Peeta with the best odds of survival, she remembers what Haymitch said to her. Her enemy is the Capitol, not the other victors. Figuring out Beetee's true plan, she ties the wire to an arrow and shoots it into the force field. The lightning strikes, sending a current upwards, destroying the dome.
As fireworks and explosions go off around her, Katniss is retrieved by a hovercraft and strapped into a hospital bed. Seeing Plutarch Heavensbee, she assumes she has been captured by the Capitol. When she fully comes to, however, she finds Plutarch has been working with Haymitch, Finnick, and the majority of the Quarter Quell tributes to break them out of the game. The hovercraft is on its way to District 13. Katniss learns that most of the districts are now in full-scale revolt. Katniss feels betrayed by Haymitch; he left Katniss and Peeta in the dark about the whole plan and now Peeta is in the Capitol's hands along with Johanna and Enobaria.
Katniss refuses to eat or talk to anyone until Gale shows up. He tells her that Prim and her mother are safe, but that District 12 has been destroyed by the Capitol.