The film opens three years before the start of the Hunger Games, during the initial rebellion in Panem. Young Coriolanus Snow (Dexter Sol Ansell) and his cousin Tigris (Rosa Gotzler) are running through the desolate streets, hiding when they witness a man eating human remains. The children return home to find their grandmother, “Grandma’am” (Fionulla Flanagan), who informs Coriolanus that his father, General Crassus Snow, has been killed, and that the family line now depends on the boy.
Part I: The Mentor
Thirteen years later, the older Coriolanus (Tom Blyth) still lives with Tigris (Hunter Schaefer) and Grandma’am, hoping to restore his family’s name. They are preparing for the tenth annual Hunger Games, for which Coriolanus has been assigned to be a mentor to one of the new tributes. He joins the other mentors, including Sejanus Plinth (Josh Andres Rivera), who comes from a wealthy family and is vocally disapproving of the Games. Head Gamemaker Dr. Volumnia Gaul (Viola Davis) arrives to introduce Dean Casca Highbottom (Peter Dinklage), the man responsible for the creation of the Hunger Games. Since viewership on the Games has been struggling, Highbottom tells the mentors to focus on having their tributes entertain the audience rather than win.
The Reaping ceremony begins, and Coriolanus is assigned to District 12, to his dismay. His tribute is Lucy Gray Baird (Rachel Zegler), who is seen in her district putting a snake down the blouse of Mayfair Lipp (Isobel Jesper Jones), daughter of Mayor Lipp (Marc Aden Gray), after Mayfair made a crude comment. Lucy Gray goes to the stage, where the mayor strikes her for harming his daughter, but Lucy Gray slowly rises back to her feet and begins to sing in defiance, which causes both people in the district and even some of the mentors to begin weeping. Coriolanus suddenly takes an interest.
As the tributes are being hauled off into a truck, Coriolanus sneaks onboard to try and talk to Lucy Gray. The other tributes, including a particularly violent one called Reaper (Dimitri Abold), suggest killing Coriolanus, until he reminds them that they will all be executed for doing so. He speaks to Lucy Gray in an attempt to earn her trust, as he hopes to make her the champion of the Games through his methods.
The tributes are placed in a zoo. Coriolanus talks to Lucy Gray and even offers her some food. He learns that she comes from a group in District 12 called Coveys that sing. She also speaks to the camera crew, led by interviewer Lucretius “Lucky” Flickerman (Jason Schwartzmann). As this happens, another tribute, Brandy (Luna Kase), grabs a bottle from her mentor Arachne Crane (Lilly Cooper), who was taunting her with it. Brandy smashes the bottle and stabs Arachne in the throat with the broken neck, leading to the Peacekeepers to shoot Brandy dead.
Moments later, Gaul takes over to announce to everyone watching that Felix Ravinstill (Aamer Husain), son of the Capitol’s president, has died after the rebel bombing, and in response, the rest of the tributes will be killed. She intends to send her snake vat to the arena, but Coriolanus makes his way to her lab by sneaking past guards and slipping his father’s handkerchief into the vat since it has Lucy Gray’s scent on it.
Lucy Gray continues to hide from the other tributes. She grabs the last unbroken water bottle and slips rat poison in there, hoping for someone like Coral to drink it. It is taken by a smaller girl named Dill (Luna Steeples), who drinks it and dies while Lucy Gray watches with horror and remorse. Reaper comes upon Dill’s body and mourns her before gathering all the deceased tributes and placing the Capitol flag over their bodies to spite everyone watching.
Lucy Gray hides in the vents, where Coral and her fellow tributes try finding her. Lucy Gray slips some of the rat poison through the vents, killing one tribute named Treech (Hiroki Berrecloth). After Lucy Gray gets out, the snake vat arrives and breaks open, releasing thousands of snakes upon everyone. The remaining tributes are killed, and Reaper accepts his fate. Coral tries to go after Lucy Gray one more time, complaining as she dies that she could not have killed all the others for nothing. With only Lucy Gray remaining, she begins to sing powerfully once more as the snakes surround her but do not kill her. Gaul initially refuses to declare her a winner, until viewers, including the other mentors, begin to chant for her victory, and Lucy Gray is deemed the winner of the Hunger Games.
Following the win, Coriolanus is brought to meet with Highbottom, who found out about the rat poison and the handkerchief. Since he had previously stated that cheating would be punishable, Highbottom banishes Snow to the districts as a Peacekeeper for the next 20 years.