The infected multiply in droves. Scrambling for their lives, Nanm On-Jo and Lee Cheong-San find safety with others inside a classroom-but not for long.
In need of a cellphone, two students take a risky journey to the teachers' office. Byeong-chan passes on critical information to Detective Song Jae-ik.
The group clears a path to Cheong-an using sound to draw away the zombies, but a new type of threat surfaces. Nam So-ju breaks out of the quarantine camp.
To make it out of the music room and onto the roof, the students put into action their most perilous plan yet. Elsewhere, Jae-ik comes across a setback.
A disturbance at the quarantine camp shifts the military's understanding of the virus. A thunderstorm provides cover as the group agrees to keep on moving.
