Choi Yeon Woo (Yoo Jun) is a high school student and a "mono" who sees the world only in black and white, with each mono having a unique "probe" soulmate who allows them to see color. Yeon Woo's probe, Yoo Han, disappeared mysteriously along with his mother, prompting Yeon Woo to search for them. His classmate Se Hyun (Hyuk) offers to help and protect him, developing a close friendship while hiding a secret that could change everything. As Yeon Woo continues his quest, other monos emerge, including a female mono searching for her own probe, while a TV producer investigates the mono-probe phenomenon. This is a 2022 South Korean drama series directed by Park Sun Jae.