Episodes 01

A group of bullies led by Son Myung-hwan from Hyosan High School attack fellow student Lee Jin-su. Jin-su falls off the rooftop and is hospitalized. His father, Lee Byeong-chan, a science teacher from Hyosan High, realizes Jin-su has developed zombie-like behavior. Some time later in Hyosan High, one of the bullies, Kim Hyeon-ju is bitten by an infected hamster in the science lab. Byeong-chan sees this and locks Hyeon-ju inside the lab, but she escapes the next day and collapses in English teacher Ms. Park’s class in a half zombie-like state. Hyeon-ju is taken to the school clinic, where she suddenly bites the school’s nurse. An ambulance takes Hyeon-ju to the hospital. The nurse transforms into a zombie and attacks several students, who all get infected and start an outbreak inside the school. Students and childhood friends Nam On-Jo and Lee Cheong-San are in the cafeteria where more infected students make their way inside and panic breaks out.

Episodes 02

On-jo and Cheong-san flee the cafeteria and take refuge in class 2-5 with their surviving classmates, including class president Choi Nam-ra, former delinquent Lee Su-hyeok, Cheong-san’s best friend Han Gyeong-su, On-Jo’s best friend Yoon I-sak, the entitled and arrogant Lee Na-yeon, Oh Jun-yeong, Kim Ji-min, Seo Hyo-ryung, Yang Dae-su, Jang Woo-jin, and Kim Min-ji. Not long after, an infected teacher makes his way into the classroom and suddenly transforms into a zombie and bites Min-ji, prompting the other students to flee and fight their way into another classroom. I-sak, however, becomes infected along the way and is thrown out the window, to On-jo’s despair. When zombies try to break in, the students use a fire hose to climb down to the broadcasting room because Ms. Park is there. Meanwhile, Yoon Gwi-nam, a bully and Myung-hwan’s henchman, hides in the cafeteria’s kitchen with another two students and a lunch lady. The school’s archery team – including Woo-jin’s sister Jang Ha-ri and her co-athlete Jung Min-jae – arrive and notice the situation at school. Senior students Yoo Jun-seong and Park Mi-jin are trapped in a restroom with infected student Lee Ha-lim, but are saved by Ha-ri and Min-jae. At the hospital, Hyeon-ju infects several other people, which leads to the virus gradually spreading throughout Hyosan.

Episodes 03

In the broadcasting room, a zombie appears outside the window, causing Gyeong-su to be scratched on his wrist. Na-yeon accuses him of being infected and they isolate him for their safety. After they isolate Gyeong-su in a corner room, Na-yeon pretends to apologise but secretly puts zombie blood on a handkerchief and applies it to his wound, causing Gyeong-su to transform and attack the others, who throw him out the window. As the students condemn Na-yeon for murdering Gyeong-su, Na-yeon walks out of the room, with a concerned Ms. Park quickly following her. Gwi-nam alone escapes from the kitchen after he pushes the others to the zombies. Hyosan’s situation makes the government impose martial law and they begin to evacuate survivors. Cheong-san’s mother goes to the school, concerned for Cheong-san’s safety. On-jo’s firefighter father Nam So-ju and his team are hiding in a government facility with Hyosan’s Assemblywoman Park Eun-hee and her associates. Elsewhere, student Park Hee-su gives birth to a baby in a playground public bathroom stall and initially abandons it before returning to reclaim it after narrowly avoiding death from a car collision.

Episodes 04

Cheong-San’s mother reaches the school, but is attacked by a zombified Gyeong-Su and devoured on the football field. After police detective Song Jae-ik arrests Byeong-chan and brings him into custody for creating the virus, Byeong-chan recounts that he was angered at the school’s indifference towards the bullies who frequently abused his son. He created a virus in an attempt to make his son stronger, only to see his son develop into a zombie, and attacked his mother, who also turned. A zombie horde attacks the police station, and Byeong-chan is bitten. Using his final moments, Byeong-chan tells Jae-ik that his laptop is in the school’s science lab with the answer to eradicate the virus and he stays behind to block the horde. After receiving the crucial information, Jae-ik and his sole surviving junior colleague Jeon Ho-chul escape the station. Meanwhile, Su-hyeok and Cheong-san attempt to retrieve a phone from the staff room and encounter Eun-Ji, a bullying victim of Gwi-Nam who was bitten but did not turn. The pair are separated by zombies. Su-hyeok returns alone to the broadcasting room with the phone. Cheong-san hides in the principal’s room, where he witnesses Gwi-nam killing the principal. He flees, with Gwi-nam chasing him. In the outside world, after losing one teammate and a politician, So-ju and his remaining teammate Kim Woo-shin evacuates the government’s survivors and they board a helicopter.

Episodes 05

Gwi-nam and Cheong-san fight in the infested school library. Cheong-san gouges out Gwi-nam’s left eye using a broken phone and throws him into the horde before escaping. Jun-yeong and On-jo retrieve a flying drone from the science lab, which they use to find Cheong-san. They send the drone outside the school and are distraught to see the destruction, including Ji-Min’s zombified parents, who attempted to reach her. All landlines and internet are shut down in Hyosan in an attempt to control fake news about the virus, as Jun-seong, Mi-jin, Min-jae, and Ha-ri enter the school’s infirmary and attempt to use a computer, before heading for the archery training center to use an emergency phone to call for help. In the outside world, while they are trying to reach Hyosan High, Jae-ik and Ho-chul seek refuge in Cheong-San’s mother’s chicken restaurant, where they find the zombified Hee-su, infected and tied up at the door, with her healthy newborn baby safely placed on a bench away from her. Jae-ik rescues the baby. Simultaneously, So-ju and his group reach a military quarantine zone. In the library, Gwi-nam hasn’t turned into a zombie and seeks revenge against Cheong-san after realising the zombies don’t notice him.

Episodes 06

The students use the broadcasting system to inform Cheong-san that they are coming for him. They use music to distract the zombies while they’re leaving the room. Gwi-nam hears the broadcast, so he follows the group. Gwi-nam encounters Su-hyeok, who refuses to give up Cheong-san, so Gwi-nam attacks him. Nam-ra helps Su-hyeok, but she is bitten by Gwi-nam. Nam-ra and Su-hyeok push Gwi-nam out a window before they hide in a room. Nam-ra also doesn’t immediately transform. Cheong-san, who earlier witnessed Gwi-nam being bitten, argues for her to be killed despite Su-hyeok’s insistence that Gwi-nam was not a zombie when he bit Nam-ra. Nam-ra stays by a window, ready to jump if she turns; Su-hyeok stays by her side. Nam-ra gradually enters a half-zombified state and has an urge to bite Su-hyeok, but regains control of herself. Unknown to them, inside the adjacent PTA room, Na-yeon is alive. The restroom survivors make it to the archery training center, but Jun-seong is wounded fighting a zombie. At the chicken restaurant, Jae-ik and Ho-chul save a young girl named Se-bin. Enlisting the help of Woo-shin and Eun-hee, So-ju manages to escape the quarantine zone and heads for the school.

Episodes 07

Nam-ra exhibits heightened senses of hearing, vision, smell, and strength, as she dives further into a half-zombified state. As the group plan to escape, they close one door of the room while another is left open, and a large barrier is created in the middle of the room. Zombies are attracted to noises made, clearing the corridor and enabling the survivors to flee all the way to the rooftop, but the rooftop door is locked by Kim Chul-soo, a school outcast who was already on the rooftop when the outbreak began. As the zombies follow the students on the staircase leading to the rooftop, Su-hyeok and Cheong-san fight them off. Cheong-san finds himself face-to-face with Gwi-nam, who appears unaffected by the fall earlier on. In the outside world, So-ju arms himself with a shotgun from the police station’s armoury and continues on his way to Hyosan High to save On-Jo. Jae-ik, Ho-chul, Se-bin, and the baby successfully escape the infested streets on a motorcycle. Jae-ik spots a survivor on a rooftop, a live streamer nicknamed “Orangibberish”, and tries to rescue him. Ho-chul, however, abandons him and drives away with the children on the motorcycle because of the zombies.

Episodes 08

After Nam-ra throws Gwi-nam down the stairs, the door finally opens. However, they are too late as a military helicopter leaves with Chul-soo, who lies that everyone is a zombie. The students make an SOS distress sign in case another helicopter arrives. In the outside world, Ho-chul and the two children return to the kindergarten with a bus. Both Jae-ik and Orangibberish jump onto the top of the bus as it drives off. They make their way through Hyosan and pick up Eun-ji. They are soon picked up by the military. At the school, during the night, the two different survivor groups bond separately. For the restroom survivors, Ha-ri teaches Mi-jin archery. The rooftop survivors gather around a campfire and talk about their pasts. Flashbacks reveal that Ms. Park was bitten while saving Na-Yeon. She decides to bring the rooftop survivors some food from the PTA after repenting on her mistakes. However, Gwi-nam bites Na-yeon upon seeing her, and he ambushes the rooftop survivors.

Episodes 09

Gwi-nam reaches the rooftop and attacks Cheong-san before Nam-ra throws Gwi-nam off the roof. After Jae-ik’s group are taken to the quarantine camp, Jae-ik reveals during the interrogation about Byeong-chan’s laptop. The military thus send a helicopter to Hyosan High, where the troops successfully takes the laptop from the school and is about to evacuate the surviving students. However, they receive last-minute mandatory orders to treat any survivors as asymptomatic and abandon them, due to a simultaneous on-camp incident where Eun-ji suddenly turned aggressive and bit Chul-soo. The soldiers reluctantly leave the rooftop survivors behind, much to their mutual distress. The soldiers and scientists study both Eun-ji and Staff Sergeant Lee Jae-joon, a fully-zombified soldier, and decides to further quarantine the evacuated Hyosan survivors. At Hyosan High, it begins to rain and thunder, which impairs the zombies’ hearing and vision. Both the rooftop survivors and the restroom survivors notice the zombies’ weakness and thus, both groups attempt to make use of it to escape. The rooftop survivors escape and reach the ground floor first and enter the parking lot. Cheong-san is shocked to see his mother, who is now a zombie, standing in front of him behind a truck.

Episodes 10

Cheong-san’s cries attract the attention of the nearby zombies, and the rooftop survivors flee. Hyo-ryung falls down while running, and Ji-min leaves her behind. Ji-min gets lost and is killed in the school’s football field. Meanwhile, Hyo-ryung is rescued by Woo-jin. Ha-ri, with her companions, reunites with her brother and they met up with the others at the auditorium. Upon entry however, Nam-ra, due to her half-zombified condition, quickly detects a huge zombie horde. During the attack, Min-jae flees outside while Jun-seong sacrifices himself to buy the others time to hide inside the sports equipment room. The next day, the survivors formulate a plan to use the sports equipment and metal carts to form a movable barricade to surround themselves while making their way out of the auditorium. As they carry out the plan, the zombie horde attacks them and Jun-yeong becomes infected. Just as the zombies are about to overwhelm the barricade, the door suddenly opens and On-jo sees her father, who has finally reached the school. Meanwhile, the military and scientists analyse the data in Byeong-chan’s laptop, and after the experts predict that the zombie epidemic might endanger all of South Korea, the military decides to bomb Hyosan.

Episodes 11

The survivors escape with So-ju, and they encounter zombies in the tennis court. Using the flares and whistle, So-ju distracts the zombies. The students are able to get out of court, but So-ju is bitten and he dies protecting his daughter. The survivors later reach the school’s construction site and stay on its balcony. Gwi-nam encounters Min-jae at the archery training center and violently attacks him. After receiving the last known location of the group, Gwi-nam kills Min-jae and goes on his way. Meanwhile, the military use drones to attract the zombies in Hyosan to their selected bombing locations, including Hyosan High. The students prepare to flee, but Gwi-nam suddenly appears and bites Cheong-san. Cheong-san pushes him off the building. Seeing that he was going to turn, Cheong-san kisses and hugs On-jo before he enters the building to distract the zombies, allowing the rest to escape from the construction site safely. While Cheong-san gets into a final standoff with Gwi-nam, the military bombs the designated locations, wiping out the zombies. Cheong-san and Gwi-nam both fell into an elevator shaft due to the impact of the explosion. Out of regret for commanding the bombing, the military commander, Jin Seon-moo, commits suicide.

Episodes 12

After the students escape, they reach an abandoned neighborhood. Nam-ra senses some zombies. The students attempt to escape the neighborhood, but Dae-su’s leg is injured, forcing them to stay and fight off the zombies. Woo-jin is bitten while saving his sister, resulting in Nam-ra killing him. During the escape, Nam-ra increasingly feels an urge to eat her friends, with voices in her head telling her to do so, and she almost bites On-jo. Driven by remorse and in order to not hurt her friends, Nam-ra abandons the group and disappears in the neighbourhood. The remaining six student survivors – Su-hyeok, On-jo, Dae-su, Hyo-ryung, Mi-jin and Ha-ri – reach an abandoned railway, where the military finally rescues them. Four months later, the government ends the martial law in Hyosan, but continues to quarantine the residents. The six Hyosan High students sneak out of the camp and return to the remnants of their school. Nam-ra, who looks well and healthy despite remaining as a half-zombie, meets up with them. Nam-ra says there are a few others like her who escaped from the school and she will be back and jumps from the rooftop, leaving the others staring after her. In a mid-credits scene, government officials are seen taking the bodies of Byeong-chan’s wife and son to another location.