Yeon Woo is a “mono” who sees the world in tones of gray, until he meets his “probe” soulmate, Yoo Han, who causes his world to explode in color. As they explore their feelings for each other, the two boys, with the help of classmate Se Hyun, dig deeper into the mysteries surrounding Yeon Woo’s mother’s disappearance. Adapted from the web novel of the same title by Sesang (세상).