Boynextdoor ! Won Yerim has one goal. Debut and shine like the stars she's always admired. As one of the top female trainees at KOZ Entertainment, she's placed in an intense training program alongside with her fellow trainee girls. Han Taesan, the cold and unreadable member of BOYNEXTDOOR, is also a trainee at KOZ and lives on the same floor of the company dorms-just rooms apart. He has a quiet personality-Yerim's opposite. But, he finds himself quietly admiring her passion, energy, and determination. His world, usually too quiet and controlled, feels strangely empty whenever she's not around.