Mysterious Parasites Drop on Earth And Mutate Humans Into Killing Machines

It's late at night when strange-looking spores begin falling from the sky all over Earth. One lands in the middle of a music festival. A larva sprouts out of it and moves to the nearest person, entering the body through his ear and causing him to pass out. Then a woman enters the room and tries to wake him up, to no avail. After she leaves, the guy wakes up and his eyes roll in a creepy way before going back to the festival. The woman sees him and tries to approach him, only for the man to suddenly transform into a tentacle-like creature with flesh blades that immediately kill her. The crowd begins to panic and running away while the the creature starts killing every person its tentacles can reach. In town, Lee tries to buy meat and the cashier Soo-in explains he forgot to ask the butcher for the price tag. Lee begins yelling with entitlement and swear he'll kill them all before leaving without buying anything. When Soo-in's shift is finally over, she leaves on her moped and notices that Lee is following her on a car. Suddenly the vehicle hits her from behind and makes her fall off the road, then Lee gets out and begins stabbing her with a knife. Soo-in manages to push him off and tries to escape, but she soon falls because of her wounds. At that moment a spore falls from the sky next to her and Lee gets sliced open, dying on the spot. Then the police show up. At the station, Detective Chulmin is told about various deadly incidents that happened in last few hours and how mysterious Lee's death is. Chulmin is shocked to hear the victims is Soo-in, who he met before, but more shocking is to hear she's just fine after being hit by a car and stabbed, in fact she has no new scars. At the hospital, Soo-in dreams of her mother, who has a new life with a son and pays Soo-in to never show up at her door again. When she wakes up, she discovers Chul-min is visiting. She tells him about the guy at the supermarket and how the stabbing felt familiar. It turns out Soo-in used to be abused by her father as a child and Chul-min was the detective to save her. After the detective leaves, Soo-in tries to remember what happened and recalls her body shaking like crazy. A few months later, a gang leader enters a club and is attacked Kang-woo, who is pretending to be an employee. A fight ensues and after lots of struggle, the gang leader overpowers Kangwoo before running out to get help. Kangwoo panics and runs through the back door, dropping the employee vest on the way out. Then he takes the bus and at the station, he sends a message to his own gang members, explaining the attack failed and he has to lie low for now. Eventually he makes it to his family home and discovers his sister Kyunghee is behaving awkwardly and that the other one isn't around. He finds his sister's phone in a drawer but it isn't working well and a pamphlet for the Sejoon church, which has a weird logo and promotes a prayer meeting happening that night. In the meantime, Soo-in is going home on a bus when suddenly she hears a painful screeching noise at the same time a strange man comes aboard. The man stares at Soo-in as he makes his way to his seat, which makes Soo-in scared and get off the bus. Elsewhere in the city, a woman invites a guy to do the dirty at her home, however he's surprised to see he's being taken to an abandoned building. As he notices that the ground is covered with plastic, a bunch of men enter the room and start discussing how to kill him. The guy takes out his phone to call for help, only for the woman to transforms into a monster and attack. Before she can hurt him, a bunch of smoke bombs are thrown into the room, allowing the victim to run away. The woman starts chasing after him, but when they reach the stairs, a bunch of special agents come in and shoot her dead. The group of men begins transforming into monsters too and a fight ensues as both groups attack each other. The agents have special nets that they use to capture the monsters and get most of them except for one that escapes through the window. As the monster runs around, he hears a high-pitched noise coming from a van. Inside he finds a man strapped to a seat with a helmet on and asks him if he's one of their kin. However, he's interrupted by Joon-kyung, who quickly opens fire on the monster. The creature gets hurt but still manages to run away. Afterward Joon-kyung and her team search the building and find a mysterious door. They break it open and are horrified to discover tons of human body parts kept in containers. The symbol from the church pamphlet is on many walls, and Joon-kyung realizes the monsters are banding together. Back at Kang-woo's house, Kyung-hee talks to somebody on the phone about recruiting Soo-in into their organization. As she leaves to go, Kang-woo secretly follows her. Meanwhile Soo-in hears the same weird noise again and sees the strange man from the bus. He begins chasing her and Soo-in runs into a junkyard, where the man teams up with Kyung-hee to corner her. As Kang-woo watches from a hiding place, the man and Kyung-hee transform into monsters. They take some of Soo-in's hair, causing her to transform as well but only partially. The duo gives her a pamphlet and ask her to join their organization, saying their kin must work together. After the man and Kyung-hee leave, Kang-woo tries to escape too but he makes noise and Soo-in finds him. She hits him before trapping him with the tentacle and learns that his sister is one of her kin, so she asks him to pass a message. Moments later, Soo-in wakes up from her possession and Kang-woo tells her everything. The night Lee attacked her, a parasite entered her body, took over, and killed Lee. However because the parasite had been so busy healing her wounds, it wasn't able to fully control her brain like it's happening to other humans. The message from the parasite ends with a warning, don't go near people that cause the noise because they're monsters. Then Kang-woo leaves, taking the pamphlet with him. When she returns home, Soo-in writes a question on a notebook before lying down. She blinks and notices several minutes have passed, there's also an answer on the notebook. The parasite has confirmed Kang-woo's words and invites Soo-in to ask questions, so writes down a bunch of them. Eventually Soo-in falls asleep and dreams of how her possessed body killed Lee. In the morning, she finds all the answers to her questions on the notebook, which she reads on the bus to work. Because the parasite failed to completely take over Soo-in's brain for good, now it can only take control for 15 minutes a day. The parasite's job now is to protect and take care of Soo-in's body since it's its home now. The parasite even left a video of the transformation on her phone as proof. At the police station, Chul-min is surprised to find a special operation going on, there are armed agents everywhere and all cops are scanned before entering. Next all the officers are taken to a room where they meet Joon-kyung, captain of the parasite special forces known as Team Gray. She explains that the parasitic organisms have appeared all over Earth and matched up with human hosts, showing video of the festival killings to prove it. She also reveals the dead body of a possessed man, which leaves everyone in shock. The parasites take control of the hosts' brains and the people's consciousness are completely absorbed, making them not human anymore. The creatures that complete their mutation follow their instincts and kill humans by making blades with their tentacles. If a parasite doesn't have a living host body it will die, so the best way to kill them is by making the host body bleed out or destroy the heart entirely. To identify them, they must pluck out a strand of hair from the host body. If the strand of hair crumbles away then there's a parasite living in the human. Next June Kyung brings out the man on the chair from earlier, who happens to be her possessed husband. The helmet has a device that dispenses a chemical capable of immobilizing parasites. It also has a sensor that monitors if the parasite transforms itself in order to escape. If this happens, the chemical dispenses and the parasite experiences a lot of pain. Parasites can use brain waves to detect other parasites that are near them, so they're keeping this one alive to use as bait and capture others. This guy has received the name Hunting Dog and when Joon-kyung presses a button on the remote, the body wiggles in pain. One of the officers wonders if this counts as torture of a human being, so Joon Kyung removes her ear, revealing it's a prosthetic. Her husband cut off the real one, so she doesn't see him as the man she loved anymore. It's not human, just a virus that needs to be exterminated. The meeting ends with Joon Kyung telling the police force to come to Team Gray with any suspicious cases they come across. Meanwhile Kang-woo takes his sister's phone to a repair shop and learns that the rival gang has been asking around him. Then he goes to a bike shop and while he tries to choose a model, the mechanic makes a call. Soon the rival gang arrives at the shop, so Kang-woo starts fighting them using any object he can find in the room. He manages to push the men off and when a second van with gang members arrive, he quickly escapes on a bike. The van begins chasing him so Kang-woo goes through the market hoping to lose them, only to fall instead. He continues to escape on foot and after taking a corridor, he manages to lock a door behind him to slow the men down. Then Kang Woo retrieves his bike and returns to the street, where he punches another gang member before finally leaving. At Team Gray's work site, Detective Won Seok brings Joon Kyung all the strange case files he could find, including Soo In's. He also says that he wants to join Team Gray. Joon Kyung tells him that if he actively cooperates, she'll put in a good word for him. During lunch break, Chul Min meets Soo In because he's worried her fast recovery may may mean she's a monster. He pretends she has something on her hair to pluck a strand but it doesn't disappear, so now he thinks she's fine. While they chat, Soo-in starts to hear the noise and sees a man staring at her, but he goes away when he sees she is company. Before leaving, Chul-min gifts Soo-in a cute keychain. After work, Soo-in is approached by Kyung-hee and the guy from the bus again, who tell her their pastor wants to see her. They force her to get in the car by threatening to hurt the humans in the area. At the same time Kang-woo wants to find his other sister, so he goes to Sejin Church and hides among the trees to record the people arriving. At that moment he notices a second building nearby and goes to check it out. Inside the church, the parasites awkwardly stand around to listen to Pastor Hyuk-joo, who they consider their leader. He plays a video message from the parasite that escaped from Jun-kyung, explaining that special forces are after them and that they have a parasite as a prisoner. He tells everyone that if they don't come up with a plan quick, Team Gray will eliminate them all. Then the parasite dies from the wounds made by Jun-kyung's gun. Hyuk-joo offers the crowd a long speech about how they should work together to bring humanity down. In the other building, Kang-woo finds tons of dead bodies in bags hanging from hooks. At that moment a guard comes in and starts looking around with the eye in his tentacle, so Kang-woo carefully sneaks around, noticing that the monster face can't see when the eye is out. On his way out, he's devastated to discover his other sister is one of the bagged bodies. After taking a moment to grieve, he furiously jumps out of hiding and attacks the guard, punching him a few times before running out of the building and locking the door. This is sensed by Hyuk-joo, who sends the crowd to capture the intruder. As the parasites move, they accidentally bump into Soo-in and cause her to drop her keys. Back to Kang-woo, he's running through the woods when he encounters the rival gang. He tries to warn them of the incoming danger, but they don't listen. At that moment Kyung-hee and the parasites arrive and immediately start killing all the gang members with their freaky tentacles. Both Kang-woo and Soo-in use this opportunity to escape and they bump into each other, so they run away together. The parasite from the bus notices someone escaped and transform into a flying shape to go after them. Kang Woo and Soo In make it to a gas station where Kang Woo had agreed to meet with a fellow gang member. They get in the guy's car and as they drive away, Kang Woo realizes his friend is a traitor who told the rivals where he was. The guy takes out a knife and tries to attack Kang Woo, so the car starts moving like crazy as the men fight on the front seats. At that moment Soo In hears the noise and the flying parasite lands on top of the car, breaking the roof. Soo In's parasite takes over and starts fighting the enemy while the car continues to shake. Using his knife, Kang-woo's friend tries to help, but a tentacle stabs him to stop him. Kang-woo then makes a sudden turn in the car to throw the flying parasite off, losing control of the vehicle in the process. Soo-in jumps off the car right before it hits a tree and hangs off a cliff. Then the flying parasite attacks Soo-in and their fight restarts in the middle of the road. The enemy realizes Soo-in is a mixed mutant and tries to fly away to warn the pastor, so Soo-in grabs him with a tentacle and smashes him the ground, causing enough bleeding to kill him before passing out. In the car, Kangwoo wakes up and hears from his friend that it was their boss who put in orders to kill him. Then the guy dies. Kangwoo tries to climb out of the car, only to slip and end up hanging off the edge. At that moment Soo-in wakes up as human and comes to help him, but she isn't fast enough. As Kangwoo falls, the parasite takes over again and saves him with her tentacles. At the police station, Joon-kyung finds Soo-in's case file and concludes she's a parasite. A flashback then shows Joon Kyung and her husband had been loading their car at the supermarket when she realized they forgot something, so she went back inside. At that moment a spore landed on top of their car and the parasite immediately came out to enter the guy's ear. Minutes later Joon Kyung saw people running around in panic and her husband calmly walking by. When she tried to approach him, he transformed and attacked her, cutting off her ear. Joon Kyung ran away and helped a kid return to the mother. Then she grabbed some toxic cleaning products and ran to the fridge. Her husband followed her, so she threw the product at him to distract him then ran out to lock the door before having a breakdown. In the present, Joon Kyung wakes up from another nightmare about the incident. In the morning, Kang Woo and Soo In are hiding at a motel. They agree they should tell the police about the church, so Soo In gives Chul Min's number to Kang Woo so he can make an anonymous call on the payphone. Afterward they also agree they need to lie low for now, so Kang Woo pretends to be Soo In's relative and calls the supermarket to say she's too sick to go to work. Then Chul Min goes to see Joon Kyung, who asks about Soo-in. Chul-min assures her that he checked her hair and it was fine before telling her about the anonymous report. Both Team Gray and the police force immediately head to the church, sending out a drone first. There are no parasites around, and Joon-kyung reminds Hunting Dog to press the remote if he senses anyone coming. The teams break into the buildings and find all the dead bodies in the bags. In the church, Chul-min finds Soo-in's keys and recognizes the keychain so he hides them in his pocket, which is seen by Joon-kyung. Later the forensic team explains all the bodies were mutilated to hide their identities. The body parts have been mixed, so it'll take a while to identify all the different DNA. The church is under Hyukjoo's name because he used to be a pastor as a human too, and his in-laws reported him and his wife missing a few weeks ago. Wonseok volunteers to go looking for him. A few hours later, Wonseok arrives at a mysterious building where Hyukjoo and other parasites are hiding with more bodies. It turns out Wonseok is working with them and he warned them to escape the church before the agents arrived. Hyuk-ju asks Won-seok to kill Hunting Dog and gives him a blade that simulates their tentacles. At the motel, Kang-woo is surprised nothing parasite-related is on the news. Soo-in receives a phone call from Chul-min asking to meet and they choose an abandoned amusement park. When Chul-min leaves the station, Joon-kyung sees him and follows him. Kang-woo goes with Soo-in to the park and Chul-min gives her the keys as he demands an explanation. Suddenly Soo-in hears the painful noise. It turns out Joon-kyung has brought Hunting Dog and he's telling her of a parasite nearby, so she enters the park. Su-In tries to run away and when Chul-Min stops her, Kang-Woo gets in a fight with him and the detective recognizes his voice from the phone. At that moment Joon-Kyung finds them but before she can shoot, Kang-Woo pushes Chul-Min to make her fall. Then Su-In and Kang-Woo run to hide inside one of the abandoned rides while Joon-Kyung chases after them. At the same time, Team Gray and the police arrive at the park. Won-Suk also comes and looks for Hunting Dog. Inside the ride building, Kang-Woo activates the game to distract Joon-Kyung but it doesn't work. The parasite takes over Soo-In and tells Kang-Woo to run while she handles this. After Kang-Woo leaves through the back door, Soo-In attacks Joon-Kyung with her tentacle to knock her down before running out too. Unfortunately she's soon surrounded by the agents. Outside, Kang-Woo watches Won-Seok repeatedly stab Hunting Dog, who is using the remote to send a warning. Joon-Kyung sees the light on the remote and thinks there's another parasite nearby, so he leaves with her team after telling the cops to keep an eye on Soo-In, who passes out. Chul-min immediately comes to her defense and tries to tell his men to lower their guns. By the time Joon-Kyung finds Hunting Dog, he's already dead and Won-Seok is gone. Kang-Woo runs away through the woods and Won-Seok sneaks into the building through the back, pretending he's always been with his team. A furious Joon-Kyung takes the helmet back into the building and after Team Gray takes Chul-min away, she puts the helmet on Soo-In and arrests her. Later at the station, the teams are having a meeting with the higher-ups from Team Gray. Joon-Kyung keeps calling Soo-In a monster, but Chul-Min demands for the test results to be shared. The x-rays and a hair sample all came out negative for parasites. Currently Soo-In's in a coma and tied to Hunting Dog's chair. The higher-ups want to learn more about the parasites before telling the public, so they order the teams to bring Soo-In to Team Gray's headquarters to run more tests. Meanwhile Soo-In is stuck in limbo between life and death. She looks around and sees her parasitic self, who Kang-Woo has nicknamed Heidi after Mr. Hyde. Heidi explains that since Su-In is on the verge of dying, she split her consciousness from the outside world. As the machines in the real world detect weird brain activity, Heidi makes Su-In some memories from her childhood. First it's the time when her father got arrested and Chul-Min saved her. People looked at her as if she was a monster for her report because a child was supposed to respect her father. The other memory shows how little Su-In tried to contact her mother, but the woman looked at her in disgust and paid her to go away. Heidi tells Su-In not to feel bad because she did the right thing and her mother was acting out of trauma since her husband also abused her. At the station, Won-seok secretly calls Hyuk-ju to tell him about Soo-in's transfer. Hyuk-ju confirms their plan is still on and goes outside to paint the organization's symbol on the door. In the meantime, two officers find clues that Kang-woo was the guy with Soo-in, so Chul-min decides to find him. Kang-woo is at the bus station reading the news on his phone, but they still don't mention the parasites. As soon as he boards a bus, Chul-min handcuffs him and drags him to his car. Desperate to buy his freedom, Kang-woo tells him about hunting dog's death. Chulmin shows him a picture of his team and Kangwoo points at Won-seok. He also tells him the truth about what's happening to Soo-in. Chulmin decides to free Kangwoo and explains Soo-in will probably be experimented on at headquarters, so he wants him to help him save her. If Kangwoo agrees, then Chulmin can protect them both. At first Kangwoo refuses, but Chulmin changes his mind by calling him a coward and reminding him of his sisters. In the evening, Kangwoo uses Chulmin's access card to enter the station and sneaks into the locker room. There he fights an officer, who easily overpowers him and starts choking him. Thankfully Chulmin had given him pepper spray and Kangwoo uses it to distract and finally knock out the guy. Then he steals the uniform and enters the container where Suin is being held. Before he can do anything, Joon-kyung passes by and announces they're leaving early, assigning Kangwoo as the guard to travel inside the container in case Suin wakes up. Chulmin notices this and wants to help, but he's stuck in the same car as Won-seok. A truck soon takes the container away as a bunch police cars follow it for protection. However when they make it to the bridge, they find it a huge traffic jam created by a car crash. This was caused by a parasite, who starts attacking and killing civilians. Team Gray immediately rushes to fight him and Joon Kyung tells the truck driver to go back before joining the fight as well. While the cops evacuate any surviving civilians, Team Gray tries to stop the parasite, only to get killed one by one by the deadly tentacles. Soon more parasites arrive to help their friend. They drive a van right into the truck to slow it down, then a parasite jumps on the window to kill the driver. Joon-kyung fails to shoot the monster down and is pushed out of the way when the truck moves on and crashes against the cars. Kang-woo comes out and sees Joon-kyung is unconscious, so he takes her remote and tries to rush back. However Joon-kyung had been pretending and immediately starts fighting him. She manages to hold him down, but at that moment the parasites throw a car with their tentacles and she has to move away. Kang-woo uses the chance to rush back into the container while the parasites attack Joon-kyung, who has to stay on the bridge and shoot as many enemies as possible. While Kang-woo starts freeing Soo-in, a parasite starts breaking down the container, only to get shot by Chul-min. Inside Soo-in's mind, Heidi reminds her some people do care and shows her a memory of Chul-min protecting her before announcing it's time to go back. At that moment Kang-woo finally removes the helmet and Soo-in wakes up. Then Kang-woo and Soo-in steal a car to escape while ignoring the shots coming their way. Won-seok quickly gets in a car and yells for Chul-min to join him so they start following the duo. However after a few miles, Won-seok suddenly takes a different turn. At the same time Soo-in begins hearing the noise and realizes Chul-min is in danger, so she leaves the car to go rescue him. Won-seok takes Chul-min to a deserted area and explains that as a cop, he saw the worst of humanity and that's why he joined the church. He thinks parasites are more rational than humans and could create a better society. At that moment Hyuk-ju shows up and Chul-min immediately starts shooting at him. But as Hyuk-ju falls to the ground, his parasite comes out and decapitates Chul-min in just one move. Then the parasite enters Chulmin's body, forming the head again. Soo-in sees all this and Heidi immediately comes out to throw a pipe at Chulmin, which does nothing. A fight ensues between both parasites as their tentacles keep on crashing. Won-seok gets ready to help his leader, but suddenly Kang-woo arrives and speeds up to run between the parasites, forcing them to split. Heidi uses the chance to jump in the car and they drive away. A flashback then shows Kang-woo's other sister Jin-hee going home after work. Her dog kept barking at Kyung-hee, who was meeting with Hyukjoo. Jinhee thought her sister was sick, but Kyunghee refused to go to the hospital and said her church was taking care of her. This wasn't good enough for Jinhee, who wanted to call a doctor. At that moment the flying parasite showed up and said they should get rid of her. Kyunghee suddenly released her tentacles and tried to attack, so Jinhee ran away. The dog attacked the parasites, only to get killed. Seeing the flying parasite following her, Jinhee ran to hid in the sewers, but unfortunately she was found. She tried sending out a message on her phone, but she got killed before she could finish. In the present, Kang-woo calls the last number Jin-hee dialed, which belongs to a friend of the family called Ki-suk. The guy won't be home but allows Kang-woo to hide there for a while, texting him the alarm password. All the messages Kang-woo sends his friend are seen by Kyung-hee, who has access to her sister's messenger on the computer. At the police station, the higher-ups give Joon-kyung three days to completely eradicate the parasite organization. That way, an upcoming festival and an important national memorial to a war hero can go off without any issues. Chulmin is also there, pretending to still be human with Wonsock's help. After the meeting, Chulmin looks at Suin's tests and realizes she's a mixed mutant. At that moment he gets a call from Kyunghee, who tells him where Kangwoo and Suin are headed. Chulmin tells her that Suin is a mutant and orders her to take care of her. In the evening, Kangwoo and Suin make it to the apartment. Suin announces that she won't escape with Kangwoo anymore, she wants to speak with Joonkyung and tell her about Chulmin and Wonsock. When they watch the news, they discover that Team Gray is finally telling the public about the monsters and promises they're getting rid of them. When Kang Woo falls asleep, Soo In takes money from his wallet and leaves. Kang Woo had only been pretending, but doesn't stop her. At the station, Chul Min and Won Seok inform Joon Kyung about their discovery of the parasites' hideout, showing a picture of the painted door. They send a few cops to watch the area and find lots of people entering a supposedly abandoned building, so Joon Kyung announces an attack at sunrise. Moments later, Joon Kyung hears a phone in the evidence drawer ringing and discovers it's Soo-in, who tells her Chul-min and Won-suk are monsters. Joon-kyung doesn't believe her, but she still asks her to meet up to talk. At the house, Kang-woo abruptly wakes up when Ki-suk arrives. He tells him Jin he had been looking for him and that she was going to send her a DM. Kang-woo checks his sister's phone and finds a message that says don't come home no matter, meaning this is what she wrote when she got killed. Feeling guilty, Kang-woo decides to find Soo-in and help her. On the roof of a restaurant, Soo-in meets with Joon-kyung and admits she's a mutant. She repeats that Chul-min and Won-seok are monsters, but Joon-kyung doesn't believe her since they helped find the parasite hideout. Soo-in tries to convince her it's a trap, but at that moment a bunch of agents come out with the helmet ready. Soo-in transforms into Heidi and jumps off the roof to escape. The agents open fire and are heard by Kang-woo, who follows the shots to find Heidi and take her away in the car. While Kang-woo drives, Heidi informs him that she won't be able to take over Soo-in's body and help her for three hours since she's been doing it too often. Then Heidi lets Soo-in return and Kang-woo shares what he's learned. Meanwhile Kyung-hee enters Ki-suk's house using the alarm password he texted. Ki-suk calls Kang-woo to tell him his sister is there, so Kang-woo begs him to run. Suddenly Kyung-hee pushes Ki-suk and takes the phone to ask Kang-woo to bring Soo-in to her, otherwise she'll kill Ki-suk. Soo-in thinks she can pretend to cooperate for three hours until Heidi is ready again, so they go back to the house. However Kyung-hee now knows she's a mutant and doesn't buy her acting. When Kyung-hee is about to attack, Kang-woo bursts in and sprays her with a fire extinguisher. This allows Kang-woo and Soo-in to run out, but Ki-suk decides to distract Kyung-hee and dies in the process. Soo-in drags a devastated Kang-woo to the car and they escape. At the station, Joon-kyung takes a strand of Won-seok's hair and it doesn't vanish, so she thinks Soo-in was lying. At that moment she gets a call from Soo-in and Kang-woo who try to tell her about the trap again. When Joon-kyung doesn't believe them, Kang-woo explains he saw Kang-woo killed Hunting Dog with a weird ball day, but Joon Kyung orders her men to begin the attack while letting the duo listen on the phone. The team breaks into the hideout and finds a bunch of parasites, who get killed one by one without much trouble. Chul Min and Won Seok even join in and kill a few monsters as well as they try to escape the building. At that moment Kyung Hee is arriving, but she decides not to get off the bus when she sees the leader has betrayed his people. Joon Kyung announces to Soo In and Kang Woo that all parasites have been killed and hangs up. The duo is confused over this until Kang Woo notices a billboard announcing the festival. They realize the parasites wanted to trick the cops into thinking their organization is over and will strike at the festival to get to the mayor. Another flashback shows how Won-seok learned the locals were worried about Hyuk-joo because he hadn't been seen in church in a week. He drove to his house and found the door open, so he came inside and found Hyuk-joo mumbling while staring at the TV. Then he noticed blood on the bedroom floor and went in to find the pastor's wife dead. As Won-seok took out his gun, Hyuk-joo transformed and brought him down with a tentacle. Then, Hyuk-joo shared his plan to take over humanity, offering to let Won-seok live if he helped him. In the present, Chul Min and Won Seok announce on a press conference that most of the parasites have been eradicated except for Soo In and Kyung Hee. He asks the public to report them if they see them and confirms that the festival and memorial will still be happening. Soo In and Kang Woo watch the conference on a phone when suddenly they get a call from Kyung Hee, who wants to join forces to take down Chul Min. The duo agrees to meet with her to make a plan. At the station, Joon Kyung is finally becoming suspicious because she can't believe Chul Min has betrayed Soo In. She confronts him about it and when he pretends he's worried about protecting the population, Joon-kyung asks him what object he tried to hide from her. Won-seok makes up an excuse and takes Chul-min away, then both men agree they must get rid of her too. Moments later, Heidi takes over Soo-in to meet with Kyung-hee while Kang-woo hides. Soo-in explains that Chul-min killed his kin as part of his plan for parasites to take over the world, but Kyung-hee doesn't care and still wants to kill him. The women raise their voices and Kang-woo comes out, only for Kyung-hee to easily capture him with her tentacles. After she drops him, they all agree to be temporary allies. Back to Joon-kyung, she asks the forensics team to study Hunting Dog's wounds and confirms it wasn't a tentacle blade that did it, just a knife that was simulating one. Later, the higher-ups assign Joon-kyung the task of investigating a new church marked with the parasite symbol, a clue they received from Chulmin. Joon-kyung is suspicious but has no choice but to obey. As Team Gray heads to the church, Joon-kyung gets a call from Heidi, who informs her of Chulmin's real plan. Jun Kyung realizes the mission is fake and the real intention was to get Team Gray out of the way so the cops could be in charge of the festival, so she orders his men to go back. Meanwhile the festival is a success and the mayor arrives with Chul Min as protection. Kang Woo pretends to be a festival goer to keep an eye on things while the women stay in the parking lot since they'd be easily recognized. Suddenly they hear the screeching noise that announces a parasite is near. Chul Min fully transforms and begins attacking anyone in his way, so the cops try to evacuate the mayor. However Chul Min quickly uses his tentacles to stop them. When Team Gray arrives, Joon Kyung sees Soo In and Kyung Hee and goes after them while her men enter the festival. Soo In immediately transforms into Heidi and tells Kyung Hee to go ahead without her. Then she uses her tentacles to make some cars move and when Joon Kyung turns around to follow the noise, Heidi knocks her down from behind. Heidi announces she only wants to survive and not to hurt anyone, then she runs away. In the festival, Won Seok pushes a food cart into Chul Min to send him into a tent, then everyone hears him open fire. When he comes out of the tent, he helps the mayor evacuate the area and Kang Woo follows them. By the time Team Gray and Joon Kyung make it to the tent, they find Chul Min's body headless. Backstage, Won Seok reveals he has the leader hidden in his jacket and releases him. The parasite jumps on the mayor's bodyguard and immediately kills him. Then he tries going after the mayor himself, only to be pushed away by Kyung Hee's tentacle. Won Seok gets ready to shoot her but Kang Woo comes in and tackles him while Kyun Hee tries to capture the leader, who is jumping all over the room until he finds a place to hide. Kyun-hee tries to tell Kang-woo to run with the mayor, Won-seok shoots her from behind. She immediately knocks him out, then she pushes Kang-woo and the mayor out of the way before bring down all the furniture to force the leader out. She apologizes to Kang-woo for his family before the leader pierces her heart, killing her. After Kang-woo and the mayor run away, the leader decapitates Won-seok and takes over his body. Then he searches for the mayor, making his head really tall to look at the whole place. When he tries to attack, Kang-woo retaliates with some fireworks from a festival stand, but Won-seok reaches out and grabs the mayor anyway. Thankfully Heidi shows up and stops him just in time. Kang-woo takes the mayor away while Heidi begins fighting Won-seok, destroying the whole room as their tentacles clash over and over. Soon Won-seok realizes he can't win and decides to run to the memorial room, where he asks Heidi to join him. She can't see that the back of his head is empty and the leader's actual parasite body is sneaking around. A new fight begins between Heidi and Won-seok that causes more destruction. The parasite jumps through a glass to knock down Heidi, then it jumps into Won-seok's body to re-energize him before splitting again so they can hide. Heidi continues to search for them but at that moment, Joon-kyung comes in with her gun. She doesn't know who she should shoot, and the parasite is approaching her from behind. Heidi releases a tentacle to kill the leader as he jumps at the same time Joon-kyung sees Won-seok's empty head on a reflection, so she quickly shoots him down. After the enemy is finally defeated, Heidi says she wants to trust humans and passes out. Kang-woo Kang-woo runs into the room to check on her and Team Gray also comes in to arrest them. But Joon-kyung orders her men to take them to the hospital because they're both human. Weeks later, Soo-in is back at a convenience store job. After her shift is over, she meets with Kang-woo, who shares that he's now working as a member of Team Gray. He also reveals that Heidi sent him a letter asking him to read it for Soo-in. Heidi's message says she's glad to have Soo-in as a host and to have failed to take over her brain. Before leaving, Kang-woo points out Team Gray would be happy to have her. Meanwhile Joon-kyung meets with a mysterious Japanese man who claims to be a journalist and expert on parasites. He reaches out his hand for a handshake, but Joon-kyung doesn't take it because she sees something weird on it.