The management company of the popular idol group A.N.JELL decided to add a new member to the group. Go Mi Nam (Park Shin Hye), the new member, has to go to the U.S. due to an urgent emergency having to have an eye job. His twin sister, Go Mi Nyu (Park Shin Hye), is a soon to be nun that is in training ends up having to take her brother's place and pretend to be a boy until Mi Nam comes back from the U.S. During the time period she pretends to be Mi Nam, she unexpectedly begins to fall in love with the leader of A.N.JELL, Hwang Tae Kyung.
Hwang Tae Kyung (Jang Geuk Suk), is the leader of the popular idol group, he's a cold-hearted, straight forward, clean freak that has lived his life alone after being abandoned by his own mother until he got into A.N.JELL. When he found out about Mi Nyu being a girl, he agrees to help and keep her identity a secret from everyone else. Will Go Mi Nyu be able to keep her identity hidden from everyone else until her twin brother comes back?