As opposed to the conventional thinking, both devils and angels are important to withhold the peace of the mortal world. The devils use punishment on human when they do something bad while angels reward humans when they do something right. So, both devil's and angels have very different way of thinking. Kyuhyun is the most outstanding devil in hell while Ryeowook is a newly graduated Angel. In a collaboration between heaven and hell, Kyuhyun and Ryeowook were summoned to a high school on earth to recruit new members. They found their potential candidates, brothers Donghae and Heechul. They have to observe and help them become a better person before they can be recruited. As kyuhyun and ryeowook were educated differently, they had a hard time getting along with each other. In the process, they made new friends, got to know more about their respective roles and eventually, love! One live in hell, the other, heaven. Is it even possible?