Detective Hwasun chases killer Sooyeon to Muji, facing a sinister sinkhole.

Hwasun overcomes sinkhole smoke hallucinations with Taehan's aid.

Hwasun searches for Doyoon amid black smoke and mutants, entering the mysterious Guseonwon.

Taehan learns survivors are trapped; risks with Park Sun-il to rescue them on 5th floor.

Hwasun risks corridor of mutants to reach infirmary; peril ensues with unexpected help.

School chaos as barricades collapse; Hwasun, Dongrim battle mutants in gym, attempt escape.