S01:E01 - Episode 1
Detective Hwasun pursues serial killer Sooyeon to Muji, encountering a sinister sinkhole with a haunting figure.
S01:E02 - Episode 2
Hwasun overcomes terrifying hallucinations with Taehan's help after inhaling the sinkhole's black smoke.
S01:E03 - Episode 3
Hwasun searches for Doyoon amid black smoke and mutants, entering the mysterious Guseonwon.
S01:E04 - Episode 4
Taehan learns survivors are trapped and takes a risk with Park Sun-il to rescue them on the 5th floor.
S01:E05 - Episode 5
Hwasun risks corridor of mutants to reach the infirmary; peril ensues with unexpected help.
S01:E06 - Episode 6
School chaos unfolds as barricades collapse; Hwasun and Dongrim battle mutants in the gym and attempt escape.
S01:E07 - Episode 7
Hwasun overcomes hallucinations with Doyoon's help, escaping school with survivors.
S01:E08 - Episode 8
Facing mutation, Hwasun survives a near-death encounter with Sooyeon.
S01:E09 - Episode 9
Tae-han rescues Sunil at the hospital, but is captured by Kim Sun-nyeo's group.
S01:E10 - Episode 10
Corpses with chest wounds and vent discoveries lead to the hospital lobby pursuit of the host monster.
S01:E11 - Episode 11
Amid suspicion and tension, they pursue the monsters with liquid nitrogen.
S01:E12 - Episode 12
Dark monsters kidnap Doyoon, prompting Hwasun, Taehan, and Sunil to uncover a shocking truth at the chemical factory while searching for her.