High school student Kim Hye In's (Lee Eun Saem) life changes forever when she becomes the sole witness to the murder of another female student. To buy her silence, she is transferred to the prestigious Cheongdam International High School, primarily attended by children of wealthy families. Hye In, who comes from a poor background, doesn't quite fit in with the other upper-crust students. Her efforts to integrate with her new environment are made more complicated when she runs into Baek Je Na (Yeri), one of the most powerful and influential students – who also happens to be the prime suspect in the murder Hye In witnessed. This draws Hye In and Je Na into a power struggle over control of the school's social hierarchy, eventually uncovering secrets they were both hoping to hide.