High-temperature doomsday arrived, and her parents said only the basement was safe. Xu Nian believed it, hiding for a year, wanting to leave even her last bite of food for her family. Until a mysterious phone call rang out, and on the other end of the line was her self from ten years in the future: "Stop waiting, go look outside the door." When she pushed open that door for the first time, what greeted her was not desolation, but familiar laughter. Separated by a single wall, what kind of truth was hidden after all?