Inside Lee Byeong-chan's science lab, a student incurs a seemingly harmless bite. Shortly after, a fast-spreading outbreak soaks the school in blood.
The infected multiply in droves. Scrambling for their lives, Nam On-jo and Lee Cheong-san find safety with others inside a classroom - but not for long.
When a zombie scratches a member of the group during a fight, Lee Na-yeon demands to be kicked out. Outside the institute, the virus takes over the city.
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.
A disturbance at the camp shifts the military's understanding of the virus. A thunderstorm provides cover as the group agrees to keep on moving.
The auditorium quickly becomes a trap for the two newly united teams of survivors. Byeong-chan's video logs reveal a drastic solution to the crisis.
Though an unexpected protector helps the group reach their next destination, Yoon Gwi-nam is hot on their heels. The army makes a terrible decision.
The students arrive at the quarantine camp, all heartbroken over their tragic losses. Months later, they cling to the hope that there are survivors.