Everyone has imagined it at least once. What if you could go back to the past?

Jang Hye Seong, a well-known painter, visits his alma mater, Seongjin High School, to give a special lecture at the request of his friend Tae Jun. During a break, he stops by the art room and discovers his old sketchbook. Inside it, he finds a drawing of his first love, Lee U Jin, half undressed.

On impulse, Hye Seong redraws U Jin right there. The moment he finishes the painting and puts the brush down, he is suddenly transported back to 2008, his high school days, where he reunites with U Jin.

Even after returning, Hye Seong doesn’t want to repeat the mistakes he made back then, so he tries to keep his distance from U Jin. But with U Jin boldly and persistently coming closer, Hye Seong is left completely defenseless.

Their eighteen begins again. Can they change their fate and finally reach each other?