Yoojin always dreams of listening to a voice of a teenage boy that is sweet and mellow. She always listens that the boy singing a goodnight song. When she wakes up, she always thought who is that boy that always sings for her in her dream? So who is the boy that sang in Yoojin's dream? What is the boy's intention towards Yoojin? Is the boy in her dream really exist in the real world? Will Yoojin finally find out who is the boy in her dream?