I am the only one who can see people’s life expectancy with the so-called “Back Number”! Wonyeong started to see the number of days people could live on their back after he barely survived a severe car accident. When the blinking red-light number falls to 0, the person dies without any exception. If so, can people live if he finds ways to save them from death? Someone who knows the secret of Back Number approaches and warns Wonyeong that he must not intervene in human life or death.