Dark Hole

Detective Hwasun pursues serial killer Sooyeon to Muji, encountering a sinister sinkhole with a haunting figure.

Hwasun overcomes sinkhole smoke hallucinations with Taehan's aid.

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.

Hwasun overcomes hallucinations with Doyoon's help, escaping school with survivors.

Hwaseon survives from Suyeon's attack with Taehan's help. After the attack, Hwaseon notices that she got a new ability. Whereas Jisoo secretely experiments on severe patients believing the black fog can be the key of developing a new treatment.

The past that plagued Dong-rim is revealed. When Tae-han realizes that Sun-il is in danger of being sacrificed, he goes straight to the hospital to rescue him.

Corpses with chest wounds, vent discoveries lead to hospital lobby pursuit of the host monster.

After finding out that liquid nitrogen can kill the monster, Hwaseon, Taehan, and Sunil run to the dermatologist. Meanwhile, Kim Seonnyeo, abandoned by the Dark Monster, turns into a mutant.

Hwaseon, Taehan, and Sunil head to the chemical factory where Doyun is kidnapped by the Dark Monster. Hwaseon and the others encounter the Dark Monster at the factory and struggle to kill it.