Yeon Woo’s probe was a boy named Yoo Han, and the two developed a beautiful friendship that blossomed into romance. But as their relationship intensified, mysterious goings-on suddenly got very unpleasant for Yeon Woo, who eventually found that Yoo Han had disappeared, with his mother also vanishing.

Yeon Woo vows to do whatever it takes to track down his “probe” and his mother. A classmate named Se Hyun learns of Yeon Woo’s quest and resolves to help and protect him – as a close friendship develops between the two students. But Se Hyun hides a secret, and Yeon Woo could be about to discover the truth… Meanwhile, Yeon Woo is not alone – other monos are nearer than he might think, including a female mono who is looking for her own probe. And a TV producer is also on the scene, hoping to get to the bottom of the mono-probe mystery!

崔延雨（洪瑜浚 飾）是一個高中生，同時也是一個「神經性全色盲 (mono)」，眼中只看得到死氣沉沉又乏味的黑白世界。但是，每一個神經性全色盲，一生中都有一個「命中注定的人 (probe)」，一種類似靈魂伴侶的存在，讓他們能夠看見世界重新染上色彩的樣貌。延雨命中注定的人是一個名叫柳翰的男孩，兩人之間的關係最後也從美麗的友誼昇華成了愛情。然而，隨著他們的感情逐漸加溫，一連串的神秘事件卻突然讓延雨墜入了深淵。不只是柳翰消失無蹤，連延雨的媽媽也不知下落。

延雨因此發誓，無論遇到什麼困難，都要找回媽媽和他命中注定的人。而延雨的同學世賢（韓相爀 飾）在知道了他的使命與決心後，便不斷地幫助與守護著他，兩人之間也產生了緊密的友誼。不過，世賢其實也有著自己的秘密，而延雨似乎離真相越來越近......。另外，延雨其實並不是孤軍奮戰——其他的神經性全色盲患者，比他想像中的還接近他身邊——他將會遇到一個也在尋找自己命中注定的人的女性神經性全色盲患者。而一位電視製作人也將出現在故事中，試著發掘神經性全色盲和他們命中注定的人之間神秘關係的真相！