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.
