Once one of the best rock climbers in his college years, Yong-nam is now a grown man who is not employed and must live with his parents just to get by. His older sister Jung-hyun keeps nudging him to clean up his act and make a better impression for their mother’s upcoming 70th birthday celebration, a moment that feels bittersweet as their family dynamic strains under the pressure of time.
For the birthday, Yong-nam pushes to hold the gathering at the Cloud Garden, quietly hoping that his old crush and fellow ex-rock climber Eui-joo works there. He feigns surprise at seeing her and, trying to impress, fabricates a story about a successful career—an evasive truth that catches up with him later, when Eui-joo becomes curious about why he lied.
The celebration is interrupted when a terrorist drives a truck close to the Cloud Garden and releases a toxic white gas. Panic spreads through the city as the cloud expands, and Eui-joo learns from a close friend that Yong-nam’s job claim was a fabrication, deepening the tension between them. The family rushes back toward safety, but Jung-hyun is quickly overwhelmed by the gas, forcing everyone to reorder their escape.
With the gas advancing, the group heads to the roof, only to discover the door is locked. Yong-nam improvises by smashing a window and using a makeshift harness to scale to the adjacent building, eventually opening the door for his family. Once assembled on the roof, they manage to hail a passing rescue helicopter with crude SOS signals, but the helicopter’s weight limit prevents Yong-nam and Eui-joo from boarding.
Refusing to surrender, they wrap themselves in improvised safety gear and move to seek higher ground. After locating a suitable building, they signal another helicopter to come, and from across the way they notice a group of students trapped in a building. They choose to guide the helicopter toward the students, sacrificing their own chance at rescue for others.
A nearby gas station explodes, sending a surge of toxic gas that forces them to flee the building before they can be rescued. Realizing that conventional routes are no longer viable, Yong-nam and Eui-joo decide their only option is to reach the tower crane—the highest point in the area. A drone appears and provides directional help, leading them toward their goal.
They sprint and climb across a series of buildings until the drone runs out of power, leaving them at a dead end. Just as despair sets in, multiple drones converge toward their location, and Yong-nam uses one to suspend a rope between buildings. The plan works briefly, but their combined weight proves too much for the drone, and they fall—seemingly to their deaths—only to survive the impact and reach the tower crane itself, where they are finally rescued by a helicopter.
On solid ground again, Yong-nam reunites with his family in a tearful moment, the relief palpable as they gather. As he and Eui-joo exchange a tentative farewell and a hopeful look for the future, rain begins to fall, gradually washing away the last traces of the white gas from the city.
