Yeon Woo lives in a grey world as a Mono—until meeting Yoo Han triggers his first Color Rush. Afraid of obsession, Yeon Woo resists, but Yoo Han won’t let go.

The miniseries follow a couple who have shared an emotionally painful past, but have a chance to rekindle their spark again. Jo Yoon Hee stars as a practical office worker who suddenly finds an opportunity to reunite with her first love, played by Jung Gyu Woon. Unfortunately he's still not quite all-grown-up.

Cheerful runner Sang Ha loves sprinting, while Jin Won chases marathon glory. Paired as pacemaker, their rivalry sparks unexpected feelings.

Yeon-woo, neurologically colorblind, sees colors through Yoo-han in a "color rush." Their connection intertwines with the mystery of his missing mother.