Han Seo Jin, Noh Seung Hye, Jin Jin Hee, Lee Myung Joo all live with their families in SKY Castle, a luxury private town where wealthy doctors and professors live. All of the women wish for their children to enter prestigious universities and are actively supporting their education.
One day, Myung Joo suddenly commits suicide following her son's acceptance into Seoul National Unversity as a medical student. The community is shocked by that and her remaining family quickly moves out from SKY Castle. However, the community is even more shocked, when Lee Soo Im and her inferior-birth family move in. Soo Im takes it upon herself to help the stressed-out children and challenging the other women of SKY Castle, whiles questioning her own 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.