A high school student dreamed of one day working as an architect. She became a victim of high school violence perpetrated by her fellow students. She dropped out of high school because of the bullying. She then planned revenge on her tormentors and also the bystanders who did nothing.
That student is now an adult. She has waited for the leader of her tormentors to get married and have a child. That child is now an elementary school student. The women who was once a victim of school violence, is now the homeroom teacher of her tormentor's child. Her cruel revenge plot begins in earnest.
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| Song Hye-Kyo | Lee Do-Hyun | Lim Ji-Yeon | Yum Hye-Ran | Park Sung-Hoon |
| Moon Dong-Eun | Joo Yeo-Jeong | Park Yeon-Jin | Kang Hyeon-Nam | Jeon Jae-Jun |
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| Jung Sung-Il | Kim Hieora | Cha Joo-Young | Kim Gun-Woo |
| Ha Do-Yeong | Lee Sa-Ra | Choi Hye-Jeong | Son Myeong-O |
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| Jung Ji-So | Shin Ye-Eun | Song Byung-Geun | Bae Gang-Hee | Song Ji-Woo |
| Moon Dong-Eun (teen) | Park Yeon-Jin (teen) | Jeon Jae-Jun (teen) | Lee Sa-Ra (teen) | Choi Hye-Jeong (teen) |
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| Seo Woo-Hyeok | Jeon Soo-A | Park Yoon-Hee |
| Son Myeong-O (teen) | school nurse | Teacher Kim Jong-Moon |
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| Oh Ji-Yul | Heo Dong-Won | Yoon Sung-Won | Park Sang-Jong |
| Ha Ye-Sol | Teacher Chu | Teacher Kang | Chairman Kim Shin-Tae |
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| Park Ji-A | Song Na-Young | Kang Gil-Woo |
| Jeong Mi-Hee | Gu Seong-Hui | Kim Soo-Han |
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| Jo Min-Wook | Kim Bi-Bi | Lee Min-Goo | Kim Nam-Ho |
| Jong Heon | Nurse Kim | doctor | Manager Han (ep.4) |
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| Lee Eun-Ju |
| pharmacist (ep.4) |
Additional Cast Members:
