After believing she had finally escaped the Liar Game tournament, the endlessly honest college student Nao Kanzaki is pulled back in for the final stage. She receives an invitation to participate after a rival, Yokoya, decides to drop out, leaving an open spot. Despite her fears, Nao accepts, driven by her concern for her partner, the genius former con artist Shinichi Akiyama, who has already secured his place in the finals. The setting for this ultimate confrontation is a secluded, opulent arena designed for a game called the Garden of Eden. Eleven players, all veterans who have survived previous rounds, compete for a top prize of 5 billion yen. The game is presided over by the Liar Game Tournament organization and its enigmatic staff, including the cool-eyed facilitator, Ellie.

The rules of the Garden of Eden are deceptively simple. In each round, players secretly vote for one of three items: a red apple, a gold apple, or a silver apple. The game is deliberately structured to reward cooperation. If all eleven players vote for the red apple, everyone wins one hundred million yen. However, the temptation to betray is immense. If only one person votes red while others do not, that single red voter loses one billion yen and is publicly named, while everyone else gains one hundred million yen. Conversely, if a lone player votes for a gold or silver apple while the rest vote red, that individual wins an enormous two hundred million yen bonus. Any other mix of votes results in financial penalties for red voters and gains for non-red voters. The game is designed to last up to thirteen rounds, with players eliminated if their debts become too high.

Nao immediately advocates for the idealistic strategy: everyone simply trusts each other and votes red every round. Her plea for mutual trust is immediately shattered when multiple players betray the alliance in the first round, revealing the deep-seated greed and fear among the group. Key returning players include the flamboyant and perpetually treacherous Yuji Fukunaga, whose loyalties shift with the wind, and the stoic yet ruthless Yokoya, who despite his earlier withdrawal, still casts a long shadow over the proceedings. The conflict deepens with the revelation that a mysterious player known as Person X is among them. This saboteur, secretly working for the Liar Game organizers, is deliberately manipulating the votes to ensure chaos and prevent the possibility of a collective win.

Akiyama, with his cold logic and masterful psychological tactics, takes the lead in countering Person X. He devises several complex strategies to identify the traitor and force cooperation. One such plan involves using a lipstick mark to track a player's vote, while another is a high-risk maneuver to reset the game by forcing a round where everyone loses money, hoping to shock the players into cooperation. Despite these efforts, Person X, a seemingly mild-mannered player named Sendo, outmaneuvers Akiyama, leading to a critical juncture where Akiyama is forced to sacrifice himself to protect Nao from elimination, temporarily leaving her without her main strategist.

Nao, however, has grown beyond the naive girl from the earlier rounds. Drawing on the lessons she has learned from Akiyama and her unwavering belief in the possibility of human goodness, she refuses to give up. With the help of other players who have come to respect her integrity, she works to unmask Person X. In a climactic reversal, Akiyama, having made a deal with the departed Yokoya to return to the game, orchestrates a final, brilliant deception. He exposes Person X not through more lies, but by creating a situation where the traitor is trapped by his own web of deceit. The final round becomes a referendum on Nao’s core philosophy. Faced with the choice between certain personal gain and a risky collective victory, the players, inspired by Nao’s example and weary of the endless betrayal, finally choose to trust. In a tense and emotional vote, every single player selects the red apple, achieving the perfect cooperative outcome and ending the Liar Game for good. The film closes with Nao and Akiyama walking away from the tournament, having not only won the money but proven that even in a system built on deceit, trust and honesty can ultimately prevail.