During 1970s Seoul, apartment construction is booming, technology advances, house sizes expand, and prices skyrocket into billions of won. By December 2023, the city is covered in concrete high-rises, but an unprecedented cold wave and a massive earthquake destroy nearly everything. Amid the ruins, only one building remains standing: Hwang Gung (Imperial Palace) Apartments, where Min-sung wakes up to find Seoul reduced to gray dust and rubble.
Inside the surviving apartment, Min-sung and his wife, Myung-hwa, try to adapt. With no power, water, or communication, residents panic while following useless emergency manuals. That night, a mother and child from the neighboring collapsed apartment beg for shelter. Though Min-sung hesitates, Myung-hwa’s compassion wins, and they take the pair in. The next day, Min-sung experiences the breakdown of morality as residents begin bartering for goods. Tensions rise when outsiders seek food and shelter, leading to violence and the death of a resident. A fire breaks out, and a man named Young-tak bravely extinguishes it, earning admiration and, eventually, election as the new resident leader.
Under Young-tak’s command, the residents vote to expel all outsiders, justifying it as necessary for survival. The outsiders resist, sparking a brutal clash at the apartment gates that ends with Young-tak’s bloody but triumphant defense. Soon, the apartment is reorganized into a seemingly utopian community with strict rules, labor-based food distribution, and security patrols. But unity masks cruelty. Patrols plunder nearby shops for supplies, mercilessly beating survivors, and begin calling outsiders “cockroaches”. Myung-hwa discovers that some residents, including one named Do-kyun, secretly hide refugees inside. Meanwhile, a woman named Hye-won, a former resident who survived outside, returns. Her arrival unsettles Young-tak.
As the community celebrates its stability, the truth about Young-tak unravels. In reality, he is a taxi driver who had been scammed while trying to buy an apartment in Hwang Gung. On the day of the earthquake, he confronted the real Young-tak and accidentally killed him during a fight. When the disaster struck, he assumed the dead man’s identity to survive. His secret festers beneath the residents’ growing fanaticism. When Myung-hwa and Hye-won uncover the real Young-tak’s corpse hidden in his old unit, they expose the impostor before everyone, shattering the illusion of order.
The revelation plunges the apartment into chaos. Young-tak kills Hye-won in a fit of rage, but before he can reassert control, the building is attacked by organized outsiders. A violent battle erupts, and explosions tear through the complex. Many residents die, including Young-tak, who crawls back to his unit and dies clutching a family photo. Min-sung and Myung-hwa escape the collapsing building as rain begins to fall over the shattered city.
Wandering through the devastated landscape, Min-sung and Myung-hwa find refuge in a ruined church. There, Min-sung gives Myung-hwa a hairpin, a remnant from their scavenging trip, and quietly dies from wounds he sustained during the night. Myung-hwa buries him with the help of other survivors, who invite her to join their community in a collapsed apartment building.
