Season synopsis
Contains spoilers for this season and earlier seasons.
At Hyosan High School, science teacher Lee Byeong-chan tries to make his bullied son strong enough to fight back. His experiment instead creates the Jonas virus, turning fear into violent hunger. When a student is bitten by an infected hamster in his laboratory, the infection escapes into the school and then the city. On-jo, Cheong-san, Su-hyeok and class president Nam-ra are among the students trying to survive classrooms and corridors overrun by their former classmates. Their friendships are tested as quickly as their barricades: Na-yeon deliberately infects Gyeong-su after accusing him of carrying the virus, and Nam-ra exposes what she has done.
The outbreak produces another danger in Gwi-nam, a bully who retains his awareness after infection. Cheong-san witnesses him murder the principal, and their fight leaves Gwi-nam with an injured eye and an obsession with revenge. His bite infects Nam-ra, who develops heightened senses and strength while struggling against the urge to eat her friends. Soldiers abandon a rooftop rescue after another apparently healthy survivor attacks someone in quarantine. The students must escape without them, moving through rain and a gymnasium where their improvised escape costs more lives. On-jo’s firefighter father reaches them, but sacrifices himself while helping them through the forest.
With the infection threatening to spread, the military orders Hyosan bombed. After Gwi-nam bites Cheong-san, Cheong-san draws the zombies away so his friends can escape; his final confrontation with Gwi-nam ends in an elevator shaft as the blast arrives. Six human survivors eventually reach quarantine. Months later, a fire on their school rooftop brings them back to Nam-ra, who has survived and found others like herself. She remains apart from her friends, although their reunion preserves the bond the outbreak nearly destroyed.