The apartment complex gets walled up and quarantined due to Min Ji's mad person disease triggered by the Next drug. Whether they like it or not, the people living in the apartments have to stay within the walls together for a week. Sae Bom and Yi Hyun isolate the suspect Ju Hyung and provide shelter for outsiders. Meanwhile, during the joint investigation, Yi Hyun and Tae Seok discover the dealer of Next lives in Building 101.