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.
One day, Myung Joo unexpectedly commits suicide following her son's acceptance into Seoul National Unversity as a medical student. The community is shocked and her remaining family quickly moves out of SKY Castle. However, the residents are even more shocked when Lee Soo Im and her inferior family move in. Soo Im takes it upon herself to help the stressed children and challenge the other women of SKY Castle while questioning her ways of supporting her step-son and uncovering the truth of what happened to Myung Joo's family and their relation to the grade coordinator, Kim Joo Young.