Han Seo Jin, Noh Seung Hye, Jin Jin Hee, and Lee Myung Joo all live with their families in SKY Castle, a luxury private neighborhood hosting wealthy doctors and professors. All of the women wish for their children to enter prestigious universities and are actively supporting their education.
Following the acceptance of Myung Joo’s son into Seoul National University as a medical student, an incident occurs, resulting in the family quickly moving out. To the surprise of Sky Castle’s residents, Lee Soo Im and her inferior family move in. After interacting with the families there, Soo Im takes it upon herself to help the stressed children by challenging the other women of SKY Castle, meanwhile questioning her ways of supporting her step-son as well. She soon starts to uncover the truth of what happened to Myung Joo’s family and their relation to the grade coordinator, Kim Joo Young.