A mother with a heart of gold navigates the cutthroat world of private education when her daughter tries to join a celebrity math instructor's class.

For the families living at Sky Castle, an exclusive residential community that's home to Korea's elite, their children’s success means everything.

Kyoko, a newly-appointed English teacher at a rural but well-respected, prestigious prefectural high school, had spent her childhood and high school years overseas before returning to Japan. Because she lived abroad for a long time, she cannot understand the old-fashioned ideas peculiar to Japan and tends to be frank about what she thinks. On the eve and the day of the school entrance examination, various incidents occur. There is the spectre of someone attempting to wreck the examination for some motive. Everyone present is a potential suspect and the truth remains shrouded in mystery to the end.