New student Su-ji learns about a ranking system called the Pyramid Game that chooses the class outcasts by voting. She must decide whether to accept it or overthrow the game.

Su-ji is being harassed when she discovers that a classmate is related to the inventor of the pyramid game. A teacher offers to help, while a blackmail scheme is revealed.

After the last Pyramid Game vote, Su-ji and Ja-eun improve their rank. Ja-eun tries to protect the new outcast, while Su-ji feels it is none of his business to intervene.

Su-ji and Ja-eun continue to seek allies in their quest to eliminate the Pyramid Game. Unable to convince their classmates, they look for options outside the school, such as the hacker Seung-hwa.

Su-ji runs into trouble when a classmate reaches a breaking point on the day of the parents' visit. Ha-rin sends a warning and Su-ji's plans fall apart due to a betrayal.

A revelation after game 15 alters the rankings and generates complaints about voting application failures. A wild game of dodgeball benefits Ha-rin, until the ball is stopped.

Su-ji gets trapped by Ha-rin's blackmail. She feels bad about keeping a secret from Ja-eun. The class goes on a school trip. Tension builds until everything explodes into a game of survival.

The students are upset about a violent attack that occurred during the field trip. A powerful alliance gives Su-ji hope. And he puts his plan to take down Ha-rin into action.

The big day has arrived. Problems arise between Su-ji and her friends. A winning move is made against Ha-rin. The audience learns about the Pyramid Game. Ha-rin finally contacts Ja-eun.

Su-ji and her classmates make one last attempt to return to normal life and a safer environment. Ha-rin and Ja-eun's story is revealed.