Soo Ji, a new student at Baekyeon Girls' High School, encounters the Pyramid Game where students rank each other based on popularity. Stuck at the bottom, she strategizes to improve her standing.
Soo Ji investigates her classmates' traits and the Pyramid Game's mastermind. She allies with vulnerable girls but her teacher is unhelpful. As the 14th game starts, truant Ja Eun returns.
Soo Ji moves up to Grade C. She breaks the promise she made with Ja Eun, but she decides to join hands with her and help the new girl in Grade F to come up with a plan to destroy the pyramid game altogether.
Soo Ji grows anxious as events unfold, fearing her plan's exposure and Ha Rin's suspicions. Pyo Ji Ae worries about potential consequences of her actions. Soo Ji coerces Hae Jun into assisting, hinting she has leverage.
During parents' school visit, Soo Ji falls into Ha Rin's trap. She tries making a pact with Do Ah while Seung Yi acts to discredit her. Ha Rin manipulates the situation with her grandmother's help. Soo Ji resorts to Plan B.
With no Grade F in the 15th game, Soo Ji changes gears to eliminate the game with Ye Lim's help. Meanwhile, Ha Rin doesn't give in to Soo Ji's hindrances and thinks of a plan to counter Soo Ji.
During a school retreat, Ha Rin is pushed into the water while practicing diving. Ja Yeon rescues her. The next day, Class Five engages in a survival game with paint guns, and the last five students face the risk of being placed in Grade F
Soo Ji decides to recruit more girls to end the game and Ha Rin for good. When Da Yeon is about to be punished for what she did to Eun Jung, their teacher tells everyone that Da Yeon has to transfer to another school.
The 16th Pyramid Game begins, and Ha Rin suggests picking a classmate who will permanently stay in Grade F. Just before a vote takes place, Soo Ji tells the class that Ye Lim was attacked and hospitalized. The class decides their fate.
Ja Eun reveals what she did to Ha Rin. The school and Baekyeon Group decide to blame everything on Soo Ji for the recent mishap. Meanwhile, Soo Ji exposes the school's corruption.
