A detective moves to the city of Muji to capture her husband's murderer. Then she finds a black-eyed men screaming, then chases him until she finds a gigantic sinkhole.

The detective accidently inhales the black fog and panics; in the middle of hallucination, a tow truck driver helps her to be back to the reality.

Hwaseon gets into a place named Guseonwon while looking for Doyun. However, Guseonwon is a place for cultists; Hwaseon and Doyun are forced to be in a point of no return. Whereas Taehan heads to Muji hospital running away from the black fog.

Taehan heads to the closed 5th floor with Sun-il to rescue survivors. Whereas Hwaseon and Doyun run away from the cultists then go to a relatively-safe place, Muji High School.

Hwaseon thinks that another dangerous being is out there inside the dark smoke and warns the others. Using herself as bait, Hwaseon tries to lure the mutants away from the corridor to the infirmary but is attacked by an unexpected enemy.

Chaos ensues after the barricade protecting the school is destroyed, and Hwaseon attempts to escape from the gym with Donglim. No Jinsu reaches the hospital with Taehan and others but makes plans to flee when his true identity is revealed.