Origin of the Jonas Virus: High school science teacher Lee Byeong-chan created the Jonas Virus. After watching his son Jin-su suffer extreme bullying to the point of suicide attempts, Byeong-chan extracted testosterone and mutated viruses from defensive mice to transmute his son's fear into unstoppable aggression. Instead, the mutated virus converted human cells into rabid, dead tissue driven purely by hunger.
Key Twists & Major Deaths: Na-yeon deliberately wipes zombie blood on Gyeong-su's scratch using a rag, causing him to turn inside the broadcast room; she later dies trying to bring food to her classmates. Nam So-ju reaches the school only to sacrifice himself at the tennis court so the kids can escape. During the climax, Cheong-san is bitten by Gwi-nam during their final showdown; knowing he is doomed, Cheong-san gouges out Gwi-nam’s eye, grabs him, and plummets down an elevator shaft into incinerating flames as military missiles obliterate Hyosan High. In the finale, the survivors settle into the government quarantine facility, and Nam-ra reveals on the ruined rooftop that she is leading a community of half-zombies living in the ruins.