Lee Jung-soo (Ha Jung-woo) is driving home for his daughter's birthday. While driving through a tunnel through a mountain, the tunnel collapses. When Lee Jung-Soo regains consciousness, he finds himself trapped inside his car, which is buried under tons of concrete and debris. All he has inside the car are his cellphone, two bottles of water, and his daughter's birthday cake. He forms a kind of special bond with the head of the rescue team, Dae-kyung, who teaches him how to survive in the tunnel.