SM Entertainment insisted on adding a new singer to EXO since the lead singer, Chen, began to have some vocal chord issues. However, the newest member, Choi Siwon, had to go to the States to get surgery just before signing the contract. His sister, Choi Jiwon, is asked to stand in for him and pretend to be her brother. Will anyone find out her secret? Will the EXO members accept her? And what happened to her mother, who mysterious