Yong-nam, once among the best rock climbers in his college years, is now a grown man who is unemployed and living with his parents just to get by. His older sister, Jung-hyun, keeps nudging him to clean up his act and make a real impression as their mother’s 70th birthday approaches. For the celebration, Yong-nam pushes to hold the party at the Cloud Garden, secretly hoping that his old crush and fellow climber, Eui-joo, is on site. To make an impression, he fabricates a story about a successful career, leaving Eui-joo surprised and curious when she confronts the truth.
As events unfold, a terrorist drives a truck near the Cloud Garden and releases a toxic white gas, triggering chaos and panic across the area. While the city reels, Eui-joo learns from a close friend that Yong-nam’s boast about his job was a lie, deepening the tension between them and sparking questions about his character and motives.
The family is jolted from their focus on the birthday as the white gas spreads, and with Eui-joo’s urging, they rush back toward the Cloud Garden. Jung-hyun is overwhelmed by the gas, throwing the entire group into a rush for safety. The situation deteriorates quickly, and they crowd onto the roof, only to discover the door is locked, trapping them inside.
In a tense bid for safety, Yong-nam shatters a window and swings to an adjacent building with little more than a makeshift harness to steady him. He manages to scale the outer wall, reach the top, and open a path for his family. From there, they signal for help with improvised SOS signals and manage to attract the attention of a passing rescue helicopter. But the weight of Yong-nam and Eui-joo aboard would push the capacity beyond its limit, forcing a heartbreaking decision to leave one of them behind temporarily.
Separated but resolute, Yong-nam and Eui-joo turn to increasingly dangerous alternatives as the gas continues to rise. They improvise safety gear to cope with the toxic environment and move to higher ground, hoping to secure a better chance at rescue. They find a taller building from which to signal another helicopter, only to witness a group of students trapped in a nearby structure that needs help just as a petrol station explodes, sending another violent surge of gas through the area.
With time running short, Yong-nam and Eui-joo realize they must reach a high point that can offer a safe escape—the tower crane, the tallest landmark in the vicinity. A drone appears on their path, providing real-time directions toward the crane and helping them navigate a perilous urban maze. They race across a series of rooftops as the drone powers down, leaving them momentarily stranded. Just when hope seems dim, more drones descend toward them, and Yong-nam uses one of them to anchor a rope between buildings, attempting a daring swing to the crane.
The plan teeters on the edge of disaster when their combined weight proves too much for the drone technology supporting the rope, and the two seemingly plummet to the street below. Miraculously, they survive the fall and clamber onto the tower crane, where a rescue helicopter finally reaches them and extracts them to safety.
Back on solid ground, Yong-nam reunites tearfully with his family, relieved and chastened by the ordeal. As he and Eui-joo exchange a grateful look, they acknowledge the possibility of meeting again in the future. The city continues to breathe as rainfall begins to descend, gradually washing away the last traces of the white gas and signaling a fragile sense of renewal after the crisis. The experience leaves Yong-nam with a renewed sense of responsibility and a clearer view of what truly matters in life.
