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.

Martial law is imposed on the city. When Cheong-san is separated from the rest of the group, On-jo leads a mission to use a drone to locate him.

The group clears a path to Cheong-san using sound to draw away 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.

Jae-ik and his crew run into a student from the school. Na-yeon works up the courage to face her peers. The group shares confessions around a fire.

The students make it to the quarantine camp, each of them weighed down by tragic loss. Months later, they hang on to hope for a survivor.