Girl Mistaken tells the story of Jessica Jung who is mistaken for a boy, after a bubble gum incident, by Kim Jaejoong, a man who mother wants him to marry a girl who he doesn't love at all. He thinks acting gay will be the perfect ploy to get his mother  to leave him alone. So his mother ask him to prove the fact he is gay and so he hires Jessica to play his boyfriend, little does he know that Jessica is actually a girl.