A deadly virus emerges at Hyosan High School, originating from a science lab. A teacher, Lee Byeong-chan, created it in a twisted attempt to give his bullied son the strength to fight back. The virus, however, mutates uncontrollably, turning people into aggressive, fast-moving zombies. The outbreak begins swiftly and chaotically within the school, trapping students in various classrooms and hallways.
The story follows a group of students, primarily led by the quick-thinking Nam On-jo and her brave friend Lee Cheong-san. Their circle includes the resourceful Choi Nam-ra, the class president, and others with diverse personalities and skills. They must navigate the horrifying corridors, using their wits and whatever they can find to barricade doors and create weapons. The series emphasizes the psychological terror and the difficult moral choices they face, often having to decide who to save and who to leave behind.
Outside the school, the situation spirals equally out of control. The infection spreads to the entire city of Hyosan. Authorities, including the military, struggle to contain the outbreak, eventually imposing a brutal quarantine that leaves those inside, including the students, seemingly abandoned. We also follow the parallel stories of On-jo’s father, a firefighter desperate to reach his daughter, and a pregnant teenager, Park Mi-jin, fighting for survival in the city.
A critical element of the plot involves a rare few infected individuals who, through extraordinary willpower or unique circumstances, retain their human consciousness despite the virus. These “halfbies” or hambies, like the aloof Nam-ra and the vengeful bully Lee Na-yeon, possess superhuman abilities without the mindless hunger. Their existence becomes a central point of conflict and a possible key to a cure, drawing the attention of government forces.
The series explores themes of survival, sacrifice, and the loss of innocence. The students are forced to mature rapidly, confronting betrayal, grief, and the darkest aspects of human nature under extreme duress. Their friendships and loyalties are tested relentlessly. After immense loss and struggle, a small group of survivors, including On-jo, Nam-ra, and a few others, manage to escape the city and reach a quarantined refugee camp.
The ending is bittersweet. While some find safety, they are forever scarred by their ordeal. The outside world remains dangerous, with the virus not fully eradicated. Nam-ra, now fully embracing her hambie nature, lives separately, watching over her human friends from the rooftops, a symbol of their fractured world and the uncertain future that lies ahead.