A popular high school student, who is the top student of her class, mysteriously dies. Six of her friends who graduated from the same elementary school attempt to track down the reasons for her death. While the six friends try to find the truth behind her death, they struggle with teenage hardships and academic pressures.
| Actor | Role |
|---|---|
 Hong Jong-hyunMin Ho-soo | Min Ho-soo |
 Park Ji-yeonSeo Yool | Seo Yool |
 Lee JoonAhn Ba-woo | Ahn Ba-woo |
| HHan Ji WooBaek Hyo-ahn | Baek Hyo-ahn |
 Shin So-yulLee Ra-yi | Lee Ra-yi |
 Kim Bo-raYoon Gong-ji | Yoon Gong-ji |
| CChoi Myung-kyungLee Sang-yong | Lee Sang-yong |
| LLee Mi-soYoo Yeo-jin | Yoo Yeo-jin |
 Yoon Hee-seokJung In-woo | Jung In-woo |
| KKim Dong-beomBae Tae-rang | Bae Tae-rang |
 Jung Woo-yeonJeong Yoo-mi | Jeong Yoo-mi |
 Go Kyung-pyoBong Il-tae | Bong Il-tae |
 Jung Kyung-hoMin Chan-ki | Min Chan-ki |
| CChoi Woo-hyeokSpeaker | Speaker |
 Nam Hyun-jooHo-soo’s mother | Ho-soo’s mother |
 Jeong Man-sikBa-woo’s father | Ba-woo’s father |
 Jeon So-minBa-woo’s date | Ba-woo’s date |
 Lee Il-hwaRa-yi’s mother | Ra-yi’s mother |
 Jo Jae-yunP.E. teacher | P.E. teacher |
| SSong Eun-jinTeacher | Teacher |