Lucy Mirando (Tilda Swinton) has just taken over her family's worldwide company from her twin sister, Nancy (also Tilda Swinton). The company was previously run by their father, who was a terrible man according to everyone whenever he is mentioned. Lucy wants to erase this image that her father and sister have created fro their company, and replace it with an image that cares for all men and animals. At her first press conference, Lucy announces a new project that will revolutionize the food industry as we know it. Mirando, her company, has found a new breed of a natural born super pig and has naturally bred it to give birth to 26 different piglets. The plan is to send each piglet to a farm in every country and have farmers raise the pig by their own natural means. She adds that this will be a competition to see who can raise the very best super pig, which will be unveiled at their grand opening. When asked how long this project will take, she answers that it will take 10 years. She says that it will be worth it because they want the pig to "taste f***king good".10 years later, in Korea, we see a 14-year-old girl, Mija (Seo-Hyun Ahn), with a giant super pig whom she calls Okja. Okja is roughly the size of an elephant and looks like one too, if not for its hippopotamus-like snout. She is also very strong and can roll down a hill into a tree without getting hurt. Mija lives alone with her grandfather on top of a mountain farm ever since her parents died. Mija loves Okja like family and takes good care of her and plays with her in the mountains where they live. The pair pick fruit together (Okja's favorite) and catch fish. Mija also whispers secrets into Okja's giant, floppy ears. When Mija's grandfather calls them home, Mija accidentally slips and nearly falls off a cliff, if not for Okja quickly catching the end of her rope. With amazing ingenuity, Okja rangles Mija back up, saving her life. Mija responds by hugging Okja. That night, while Mija and her grandfather eat dinner, her grandfather mentions that Mr. Mundo, Mirando's representative that checks in on Okja's growth, will be coming the next day. Mija asks if her grandfather paid Mundo the money so they can keep Okja and her grandfather says he did. Mija goes to sleep in Okja's massive arms.The next day, Mundo arrives with the renowned and television famous zoologist, Dr. Johnny Wilcox (Jake Gyllenhaal), who is there to examine Okja in order to determine if she will win the contest. Upon arriving, Mundo asks Mija to fetch Okja's black box, a small device that is attached to her ear which monitors her health. Wilcox is loud, obnoxious and is not happy about climbing a mountain in order to reach the pig, but is speechless upon seeing Okja. He barks orders for his crew to start filming as he proclaims that Okja is definitely the winner and will go on to New York City to be unveiled for the contest. Mija and her grandfather don't speak English and can't understand what he's saying, but Mija understands "New York". After talking with Mundo, Mija's grandfather takes Mija to see her parents' graves while the crew runs a few tests and examinations. While there, Mija's grandfather gives her a small golden pig made of real gold and reminisces about how in the old days, elders gave a golden pig to girls who were getting married. He gives her the pig as a sign that she is growing up and should stop playing with a pig in the mountains every day. Mija asks him what's going on and her grandfather admits that the people have come to take Okja away and he was hoping that she would be happy with the golden pig. He explains that Okja will spend the night in Seoul before boarding a plane to America for the contest. When Mija asks about the money he used to buy Okja, her grandfather explains that Mirando wouldn't sell them the pig, so he used the money to buy a golden one instead. Mija is angered by this and runs away. Later that night, she packs a few small items, the golden pig, and Okja's fruits into a fanny pack, along with every coin she has saved in her piggy bank and tells her grandfather she's going to Seoul. Her grandfather tries to stop her and tells her that Okja's fate is to be killed and eaten, but Mija doesn't budge.Mija takes buses and subways until she finally gets to the Mirando company building stationed in Seoul. She knocks on a big glass door and asks an obnoxious receptionist to see Mundo, bu the receptionist just calls security to send someone up to escort Mija away. Determined, Mija breaks through the glass door and runs through the office building as security chases her. She finds plenty of pictures of Okja, but not Mundo. She looks outside and sees them loading Okja into a truck. Mundo takes a few pictures with Okja and has her strapped in with a few animal handlers. Okja clearly does not want to go. Mundo gets into the truck's cab with a young driver who doesn't like his job and is annoyed at Mundo's peppiness. As they drive away, Mija comes up close behind. Amazingly, she runs at pace with the truck and climbs aboard banging on the walls so Okja can hear her. Okja does and wails loudly. Suddenly, another truck drives up alongside Mirando's truck. The driver of the second truck and passenger are wearing ski masks. They cheeringly tell Mundo and the Mirando driver that they're not terrorists and hate violence and ask them to stop. When the message doesn't get across, the two men sigh and slam their truck into Mirando's stopping it and knocking Mija off. They exit their truck along with other people in masks as they open the doors to Okja and disarm the handlers. Once they break Okja out of her chains, she goes wild and rampant as the masked crew tries to calm her down. While this is happening, their leader sprays words onto the front of Mirando's truck. Suddenly Mija calls out to Okja and they run to each other and escape. The masked leader sees Mija and tells his crew to get in the truck and follow them. Mundo is upset, but the truck driver is laughing because "Mirando f***ked up, not him". Mundo orders the handlers after Okja and the chase begins. Mija leads a panicked Okja through a shopping mall in an effort to evade the police and Mundo. After crashing into a store, the masked men come in and defend Okja from the police. They pick up Mija, who is badly injured, and explain to her that they're the good guys with A.L.F. (Animal Liberation Front), an animal rights group that have been organizing attacks against food companies and slaughterhouses like Mirando for 40 years and hate violence. They all run with Okja into their truck as they escape the authorities.) As the truck drives, Mija sits with Okja as the thieves wonder what to do with her because she doesn't fit in with their plan. Their leader steps forward and takes off his mask and introduces himself as Jay (Paul Dano). His fellow members do the same and introduce themselves. K, (Steven Yeun) a Korean who acts as Mija's translator, Blond (Daniel Henshall), a big wisecracking man, Red (Lily Collins), a snarky woman, and Silver (Devon Bostick), a man who is so devoted to nature that he refuses to eat because it will leave a carbon footprint, which ends up making him sick most of the time. Mija introduces herself and Okja through K's translation. When asked how long she's been with Okja, Mija tells them since she was 4 years old, making it all of Okja's life. Touched, Jay decides to explain to her that Mirando lied when they said Okja and her mother were born naturally when they really were from a petri dish in New Jersey. He takes out a black box, similar to the one on Okja's ear, and tells her it's really a camera so they could switch it with Okja's black box and reveal to the world what really happens in the factories that Okja is going to. The contest is just a publicity stunt while all of the pigs, way more than just 26, are to be processed and chopped up to be sold worldwide. Knowing how dangerous this mission is and how much Mija cares for Okja, Jay asks her for permission to use Okja for the mission. The rest of the crew is dismayed when they hear this because it will be all of their hard work down the drain, but Jay is adamant because Mija is Okja's family. They relent and K asks her in Korean if she will let them take Okja for the mission. Mija says no, but K doesn't want to abort because they're so close and lies and tells them she said yes. Jay and the crew are ecstatic and hug her, telling her it's for a good cause. They switch out the black box and open the doors to the moving truck as it passes over water and jump out. K, who feels slightly guilty, quickly tells her to learn English before leaving Mija with Okja as the police move in. Back in New York, Lucy is not happy about the YouTube videos showing Mija and Okja running through the shopping district. Her board of directors and family lawyer, Frank (Giancarlo Esposito), tell her that it's only a minor setback and shouldn't really disrupt sales. They also mention that the A.L.F. won't be able to touch them in New York because they have beefed up security, and they failed because Mirando has Okja. However, Lucy rewinds the tapes and points at a shot with the police taking away Mija, exclaiming that the image she had worked so hard on to create for the last 10 years. They can't be a good company that loves people and animals if they're seen taking a child away from her pet. Frank calmly suggests the idea of bringing Mija to New York, and Lucy shoots up. She quickly tells her assistants to book Mija tickets, passports, visas and provide her with everything she needs and then some. Mirando will pay for whatever damage Mija caused and welcome her to New York like a hero. Lucy envisions the whole ordeal as touching as they reunite a girl and her pet onstage, like a fairy tale. Lucy says they can even make her the new face of Mirando in their marketing campaign. Dr. Wilcox, who's been listening, gets upset because he was supposed to be the face of the company that everybody loves. Lucy tells him to shut up because his ratings have been suffering and he's a has-been. Wilcox is upset at this, but Lucy doesn't care as she barks orders. Her assistant, Jenny (Shirley Henderson), makes all the arrangements as Mija is released from jail and is prepped to go to America, the company representatives telling her grandfather that she will make them a lot of money, and a lot of photo ops as Korea sends their little farmer princess to New York. Mija, who at this point does not trust anyone and is very angry, constantly demands to speak to Okja on the phone, much to everyone's confusion. Meanwhile, the A.L.F. are following Okja's signal through their black box camera and are getting the video feed. They are all excited that they will soon unveil what really happens behind closed doors. In a darkened room that looks like it was from the set of the Saw movie franchise, a drunk Wilcox has handlers bring Okja in using cattle prods. He is very upset that this pig will be taking away his fame from the company and acknowledges that while Lucy said Okja isn't to be harmed, he won't kill her. As A.L.F. watches, Wilcox brings a bigger super pig into the room to forcibly mate with Okja. As the handlers and Wilcox mistreat the pigs, A.L.F. watches in horror. Red exclaims that they shouldn't have sent Okja there since they knew what was going to happen. Blond tells her they didn't know, but Red tells him they had an idea. When she asks aloud why Mija would have agreed to this, K admits that she didn't. After he explains himself, Jay calmly walks over and punches him, which shocks the group because they don't like violence. Jay tells K that he is now banned from the group and they will return his equipment when they are done. K leaves in shame. Wilcox, meanwhile, is preparing to use a device that extracts meat from cows without killing them, as the phone rings. It's Jenny with Mija who has been demanding to speak to Okja. Hearing her voice, Okja howls and scares Wilcox who smashes the phone in fear. Upset because he too loves animals, or so he says, Wilcox extracts sausage sized meat from Okja to be grilled immediately. Mirando films people eating the meat and loving it.Lucy hears from her sister, Nancy, who is in London. Nancy taunts Lucy for the debacle in Seoul and Lucy taunts her back. Mija, who has taken K's advice and has been learning some English, is getting dressed by Mirando's stylists. Jenny gives her an outfit to wear, but Mija won't do anything until she sees Okja. Annoyed, Jenny tells her that they own the pig and if she plays ball, then she can see Okja. Upset, Mija goes into a room to change, only to find Jay standing there in disguise. By using signs with translations on them, Jay tells her that they're sorry for what they did. He tells her that they are going to free Okja during the ceremony and will take Mija and Okja home. He warns her not to look back at the TV screens since they plan to show everyone what they filmed, and Jay doesn't want to expose all that to Mija, especially after all that she's been through. He tells her that the group loves her and will be with her, giving her hope. Jay slips out the window and makes sure everyone's in position. Lucy receives flowers from Frank as congratulations for running the company for 10 years. Lucy says that she does feel guilty about lying to everyone about where the pigs really come from, but it's for the best since people freak out over genetic mutations. When Frank reveals that Nancy is in town and that the flowers are from her, Lucy gets upset. She made it clear Nancy had to stay away because Nancy scares people since she reminds them of her father.The ceremony starts with Wilcox cheeringly introducing the health the pigs have to offer and little sausages are passed around the rally from the super pigs, which everyone loves. He then introduces Lucy, who takes a few swipes at how her sister ran the company, before introducing Mija onto the stage. Mija doesn't care about any of the celebration as she looks for Okja, whom Lucy announces. A float with a tent comes forward to the stage and Mija steps forward pulling out some of Okja's fruit. Okja's snout comes out and sniffs, but then gets enraged and wails, rushing out and scaring everybody. Mija tries to calm Okja down, but Okja is wild and angry. Red marks are all over her body and her eyes are bloodshot and veiny. Jay gives the word for the video to be played and steps onto the stage in an effort to help Mija control Okja and to keep her eyes away from the screens. The crowd is horrified by the video of Wilcox mistreating Okja and boo and throw things at him. In a restaurant nearby, Frank, who is with Nancy notes the debacle and suggests that Nancy step in, to which she agrees. Okja is still running wild and bites Mija. In anger out of Okja's violence and to save Mija, Jay runs to hit Okja, but Mija stops him. Jay sees that Okja has calmed down and gets his crew ready to move as Okja nuzzles Mija and licks her wounds, literally, as Mija whispers into Okja's ear. Suddenly, the Black Chalk, Mirando's elite security squad rushes in, forcing everyone to flee. Jay and his crew try and lead Mija and Okja away, but get cornered and beaten by the squad. Just when all hope is lost, a truck pulls up and saves the pair. Lying down and bleeding, Jay sees that it is none other than K, who has come back despite Jay's ban. When asked why he shows his tattoo of their credo and rushes them to medical care as they drive to the factory. When Mija awakens and asks where they're going, Jay tells her they're going to get Okja. Lucy, meanwhile, is devastated that her publicity failed as chaos reigns in the streets. Nancy walks up and tells her that she forgot what a loser Lucy was, and remarks that while their father was a terrible man, he was a brilliant businessman. Lucy tells her to have fun cleaning up her mess, to which Nancy replies she can dress up as Lucy and go in front of the press to make a public apology. She tells Frank to start killing the pigs immediately, even Okja.At the factory, Jay tries to hold Mija back from the horrific sight of hundreds of super pigs being corralled by electric fences and cattle prods, but Mija doesn't care. She, Jay and K begin searching for Okja as security rushes to find them, with Black Chalk only minutes away. Mija finally finds Okja as she is being herded into the factory. Mija rushes in to see dead pigs being hung, stripped and ripped in half. She runs up to where a worker kills the super pigs and loads them onto a conveyor belt. As Mija watches in horror, Okja is led towards the worker to be killed. Mija yells for him to stop and produces a picture of her with Okja when they were younger and Okja was no bigger than a pet dog. As the worker stares at the picture, Nancy, Frank, Jay, K and the Black Chalk come in. Jay tries to protect Mija but is apprehended along with K. In English, Mija asks Nancy why she wants to kill Okja. Nancy haughtily tells her that people won't eat pigs unless they're dead and that she owns Okja and can do whatever she wants. As Jay and K are being led away, Jay tells her that while he cares for every living creature, both human and non-human, she is the exception. Nancy doesn't' care and gives the order to kill Okja. Mija cries out for her to wait and produces the golden pig her grandfather gave her. Mija says she wants to buy Okja, alive. Nancy agrees to the deal and tells Frank to arrange safe passage for Mija and Okja to go home. As they are led outside, Mija looks back to hear the killings have continued and all of these pigs will suffer the same fate. She then notices two super pigs struggling to lift the electric fence just enough so their baby can get out. The baby squeals and begins to make a ruckus, and Mija looks to hide the piglet before the guards can see. Quickly, Okja opens her mouth and hides the piglet inside before anyone notices.Back in Seoul, Mija lives in harmony with her grandfather, Okja, and the piglet, who has become an adorable addition to their family. Okja motions to Mija, who puts her ear next to Okja's mouth. Okja whispers and Mija smiles.In America, Jay is released from prison and is greeted by K. On a public bus, K tells him that their numbers have grown and how excited they are about their next job. He introduces their newest member from Seoul, the former Mirando truck driver, who is a gleeful addition and is quite the chatterbox. The former driver sits down next to Red, Blond, and Silver who are also on the bus. K tells him that they are almost at their stop and Mirando will be there too, including Nancy. Jay gives the signal and everyone on the bus puts on ski masks.