Once a top college rock climber, Yong-nam is now a jobless adult living with his parents, constantly reminded by his older sister Jung-hyun to pull himself together as their mother’s 70th birthday approaches. To keep up appearances, Yong-nam pushes for a birthday celebration at the Cloud Garden, where he secretly believes his old flame and fellow climber Eui-joo is working. He pretends to have a thriving career, hoping to impress her, and his lie catches her attention in a way that reveals more questions than answers.
Meanwhile, a terrorist attack unfolds as a truck parks by the Cloud Garden and releases a toxic white gas that spreads rapidly through the city. Eui-joo learns from a friend that Yong-nam’s assurances about his life were untrue, and she grows curious about the real reasons behind his sudden show of success. The rest of the family only learns of the danger when the gas begins to converge on their location, forcing them to move quickly toward safety.
As panic erupts, the family races back to the Cloud Garden, but they find the premises compromised. Jung-hyun is overwhelmed by the toxic surge, and the door to the rooftop is locked, trapping them momentarily. Yong-nam improvises a bold rescue by shattering a window and using a makeshift harness to rappel to an adjacent building. He reaches the top and opens the roof door for his family, who assemble on the roof and call for help with crude SOS signals. A rescue helicopter eventually appears, but the weight of Yong-nam and Eui-joo prevents them from boarding. The desperate group chooses to stay with the ascent, wrapping themselves in improvised safety gear to reach higher ground.
With the immediate danger still looming, Yong-nam and Eui-joo set out to signal another passing helicopter. They divert their attention to a group of students trapped in a distant building, guiding the helicopter away from themselves to save others. Just as a gas station nearby explodes and a new wave of toxic gas sweeps through the area, they are forced to abandon their current shelter and press on.
Realizing that the only viable escape route is to climb toward the tower crane—the highest nearby point—they follow the drone that appears overhead, using it to navigate toward the objective. After sprinting across rooftops and battling failing power in the drones, Yong-nam manages to lash a rope between two buildings, enabling a dangerous swing toward the crane. The strain proves too much for the drone, and the couple plummets, but they survive the fall and finally reach the tower crane, where they are extracted by a rescue helicopter.
Back on solid ground, Yong-nam tearfully greets his family, and he and Eui-joo exchange a hopeful look for a future they might share. As they pause to say farewell, rain begins to fall, helping to dissipate the last of the white gas and bringing a quiet sense of relief to the city. In the end, the ordeal redefines Yong-nam’s priorities, blending a renewed sense of responsibility with the possibility of reconnecting with someone from his past.
