On the other hand, Go Eun Byul (Kim So Hyun) is the most popular girl at Segang High School, the most prestigious private high school in Seoul’s Gangnam District. Eun Byul’s best friends are Cha Song Joo (Kim Hee Jung) and Lee Shi Jin (Lee Cho Hee), and she shares a mutual attraction with Han Yi Ahn (Nam Joo Hyuk), the school’s star swimmer. But Eun Byul has secrets, including one involving a girl named Jung Soo In.

Eun Bi and Eun Byul look exactly alike, but only Eun Byul is aware of the other’s existence.

One day, on a school field trip to Tongyeong, Eun Byul mysteriously disappears. At the same time, Eun Bi gets unjustly expelled from her school and transfers to Segang. The injured and amnesiac Eun Bi is mistaken for her doppelgänger Eun Byul, and she starts living the latter’s charmed life, unaware of the secrets Segang holds.