Joon-soo leas that his buddy Hee-gyu sister Hee-jin has no the place to go after being scammed, so he suggests residing with him. The 2 begin residing collectively. They're shut like brother and sister however they'll by no means be that. The 2 begin getting humorous and Joon-soo cant fall asleep on the considered Hee-jin sleeping only a wall away from him. Mi-na, Joon-soo girlfriend notices Joon-soo altering and seduces Joon-soo at his home the place Hee-jin is. Is it the girlfriend or the sister?