Alan Clifford, the former leader of an underground human fortress, is put on a public trial by the very survivors he protected for 30 years. His adopted daughter, Cindy, now siding with a woman named Donna, accuses him of fabricating the ongoing giant threat to maintain power. They present footage showing a seemingly safe surface, turning the gathered crowd violently against Alan. As the mob demands his execution for his alleged lies, Alan defiantly warns that leaving the fortress will lead them all to be devoured by the giants.
A mob demands the execution of the corrupted leader, Alan, from fortress guardian Ms. Clifford, hoping it will allow them to return to the surface. Despite pleas from others seeking refuge, Clifford sacrifices his own lifespan to expand the fortress capacity. Alan's secretary, Jane, reveals the hopeful surface video is 30 years old and warns everyone will die if they leave. The crowd, led by Alan's daughter Cindy, accuses Jane of being corrupted and arrests her. To prove the truth, Cindy orders a live-streamed expedition to the surface, forcing everyone to confront the reality outside.
Inside a survival fortress, the leader Chelsea pressures a prisoner named Alan to plead guilty to save his secretary. Alan publicly counters that Chelsea herself sacrificed her husband to gain entry, calling her integrity into question and causing unrest among the onlookers. He reveals she once propositioned him for power, but Chelsea vows revenge. As an expedition team heads to the surface to prove Alan is lying about the outside danger, Alan chillingly predicts they will all die first, leaving the group's fate uncertain.
A group of survivors emerges from an underground shelter to find their city still in ruins, contrary to the promised beautiful landscape they saw in videos. Chelsea confronts a woman who defends Alan's warnings, insisting the giants are gone and the doomsday has ended. Fueled by a desperate desire for freedom, Chelsea rallies the people to establish a surface camp and leave their 'cage.' As they prepare to move, a giant senses their presence nearby, having waited for a meal, and discovers the open underground fortress.
A group of rebels seizes upon footage showing a peaceful, restored surface world to condemn Alan, their leader who confined them underground. Convinced Alan lied about an ongoing apocalypse to control them, the rebels, led by Ms. Clifford, sentence Alan and his ally Jane to death and prepare a public execution. Unknown to the celebrating rebels, a hidden threat referred to as Three-Eyes observes their planned exodus, anticipating a 'feast' as the unsuspecting humans prepare to leave their fortress.
An angry mob demands the execution of Alan, a fallen leader, and his elderly parents. Alan's parents plead with their adoptive daughter, Cindy, who is now the community's leader, to show mercy and release her father. Cindy is pressured by another leader, Chelsea, to uphold her oath to prioritize the people over personal ties. Torn between duty and family, Cindy ultimately refuses her parents' desperate pleas and orders the guards to arrest them, leaving the old couple at the mercy of the unforgiving law.
In a community where humans are hunted, a man named Alan is publicly accused of murdering his friend Joseph for power. A group of his former allies, including Sherry and others, confront him with a will they claim proves his guilt. As the angry crowd denounces him, Alan's lone defender, Jane, is shouted down. The high-ranking rebels who orchestrated his overthrow now lead the mob back to the trial square, where Alan faces imminent torture.
In a sealed fortress where humanity has survived for decades, a group receives news that a woman named Donna has found a perfect lakeside location for a new base, sparking hope for a long-awaited exodus to the surface. Amid this optimism, others remain focused on a prisoner named Alan, whose trial is concluding. They express contempt, arguing his crimes are already clear and that a public vote will determine his execution method, dismissing the trial as a waste of time.
The community assembles for a vote on Alan’ long-awaited execution. Ms. Clifford and others, angered by his decision to trap them underground, argue a public hanging is too slow. They propose a swifter punishment: leaving him imprisoned in the fortress while the rest escape to the surface and detonate the entrance. The crowd overwhelmingly agrees with this new plan. After confirming everyone but Alan is out, Ms. Clifford orders the entrance blown up, sealing his fate as they celebrate their freedom.
After sacrificing his life force to protect humanity in an underground bunker for 30 years, Alan Clifford is betrayed. His adopted daughter Cindy and her ally Chelsea fabricate evidence, frame him, and turn the populace against him. Condemned to death, he watches as the people he saved destroy their only sanctuary and rush to the surface. There, they fall into a deadly trap laid by giants. As the slaughter begins, Alan—now a master of powerful mecha technology—faces a final, agonizing choice: should he save the very humanity that condemned him?