A high-teen mystery thriller about a close relationship between teenage girls in a harsher survival competition than entrance examinations.
Seul-gi, who went missing as a child and grew up in an orphanage, transfers to Chaehwa Girls' High School in Seoul to find her father. Then, Jae-yi, the top student in the school and the object of everyone's admiration, approaches Seul-gi...
A past exam question from a prestigious academy submitted by someone is the same as the math grade test taken. Seul-gi heads to the prestigious academy as if possessed. She meets Jae-yi there. Can she trust Jae-yi?
Jae-yi gives Seul-gi a new school uniform as a gift. Seul-gi, who had been wary of Jae-yi, finds out about Jae-yi's unexpected side and her heart is unlocked. She decides to go back to sitting next to Jae-yi.
After the class president election, Seul-gi, who has become close to Jae-yi ends up sleeping at Jae-yi's house. Seul-gi wakes up to the sound of Jae-yi's phone constantly ringing, and when she finally opens it, she is shocked!
A copy of Seul-gi's essay, the only one to receive an A+, is found in a drawer of a classmate's desk, and Jae-yi gets upset and tells her not to let anyone read it, but for some reason Seul-gi doesn't seem to care.
Seul-gi is disappointed that Jae-yi approached her for another reason. Before she knows it, the midterm exam is approaching, and Seul-gi, who has run out of medicine, obtains it illegally because she cannot get it prescribed at the hospital.
Seul-gi, who became the top student in the entire school along with Jae-yi, is suddenly threatened by Byeong-jin and is worried that drugs will be detected during the health checkup. Seul-gi approaches Jae-yi, who calls her up to the rooftop.
The school is in the middle of a festival, and Seul-gi is trying to trust Jae-yi again. For some reason, Jae-yi looks for Do-hyuk's phone, and there is a shocking video on the phone she gets her hands on.
Jae-yi, who learned the whole story of the incident, encounters an unexpected person in the printing room. Meanwhile, Seul-gi, who was stabbed, is taken to the hospital by Tae-jun, where she witnesses Tae-jun's eerie secret.
The school is investigated by the police due to the festival incident, and the victim, Seul-gi, is accused of being the perpetrator. When Seul-gi is put in danger because of Ara, who is cornered, Jae-yi makes a choice.
Seul-gi and Jae-yi search for the missing Je-na. Jae-yi finds out that Je-na had a conversation with Kyung-yi on the festival day and questions Kyung-yi. Then, he gets a call from Kyung-yi, who says he knows Je-na's whereabouts and offers a deal!
Jae-yi hears that Je-na had the fake ID card that Byeong-jin was looking for. Then, Jae-yi gets a phone call. Je-na is dead?
Seul-gi, who had been suspicious of Je-na's death, finds out the whole story of the case while looking for Soo-jin and begins to cooperate with Jae-yi. Kyung-yi and Ye-ri each approach the case in their own ways.
Seul-gi and Jae-yi try to find Je-na and make her a witness in court. However, when Tae-jun threatens Seul-gi's life, Jae-yi promises to become the daughter her father wants. Has Jae-yi really abandoned Seul-gi?
During the final exam, the rankings of the entire school change drastically, and Seul-gi is frustrated because she cannot figure out Jae-yi's intentions. As Jae-yi said to use Seul-gi, Tae-jun makes a deal with Seul-gi by offering her a killer college entrance exam question.
Seul-gi and Jae-yi, who have different plans, clash, and Jae-yi ends up betraying Seul-gi and going ahead with her own plan. What was Jae-yi hoping for?
