Xiao An and Mao Cai live in the same dormitory and meet one another because of their accidentally swapped bed-sheets. They grow closer by meeting frequently, to the point that Mao Cai asks Xiao An to be his little brother. Although what Xiao An feels is way more than brotherly love, he accepts Mao Cai's request. While both of them are trying to figure out their feelings, Lao Si (Xiao An's roommate) is getting into the picture too, making everything even more complicated.