*CUT TO THE CHASE*
NOTE: This spoiler was submitted by Jeremy
New York City, 2007 - Lucy Mirando (Tila Swinton) speaks to a board of investors at her inauguration as the new CEO of the Mirando Corporation. She addresses the issue of a dwindling food supply, and she offers a solution. A creature known as a super piglet was found in Chile and brought back to the United States to reproduce up to 26 super piglets to be bred in different parts of the world for the next ten years until they are ready to eat. Lucy has brought on TV personality/zoologist Dr. Johnny Wilcox (Jake Gyllenhaal) to be the face of her company. She promises to everyone that the pigs are non-GMO and are eco-friendly in an effort to bring goodwill toward her company after the bad reputation brought on by her grandfather, father, and twin sister Nancy.
Ten years later in South Korea, a girl named Mija (Ahn Seo-yeun) is living with her grandfather Heebong (Byun Hee-bong) and her pet super pig, Okja. Mija and Okja go around their home together to gather fish for supper. At one point, Mija tries to get Okja to cross a thin path, leading her to fall while holding onto a rope attached to Okja. Okja struggles to pull Mija back up. She runs toward a rock with Mija still hanging on so that Okja may jump over and pull Mija up. Okja falls down into the forest, but Mija finds her in fine condition.
The next day, a man named Mundo (Je-mun Yun) guides Wilcox and his crew make it up the hill to Mija's home so they can find Okja. He complains about the long walk up the hill and being dehydrated. Wilcox sees Okja and is amazed at how she looks.
Heebong brings Mija to the graves of her parents. He presents her with a solid gold pig statue that he purchased as he was unable to buy Okja. Mija becomes enraged when she learns that Okja is being taken back to the Mirando facility in Seoul. Against her grandfather's orders, Mija grabs whatever money she can and heads to rescue Okja.
Mija finds the Mirando facility and manages to break into the place by body-slamming against the glass door. She spots Okja being hauled into a truck and she rushes to save her.
Mija runs after the truck through the streets until she reaches it. She hops onto the back and latches on. Another truck with masked people inside drive alongside the Mirando truck and order them to stop the truck. Once they ride under a tunnel, the second truck slams into the Mirando truck and forces them to stop. The masked people hijack the truck to break Okja out. They are activists from the Animal Liberation Front (ALF), led by Jay (Paul Dano), with his cohorts K (Steven Yeun), Red (Lily Collins), Blond (Daniel Henshall), and Silver (Devon Bostick). Okja breaks free and finds Mija. She runs to the girl and Mija helps Okha run through the subway, frightening civilians. Mija is knocked off Okja as she crashes through a gift shop. A team of officers attempt to subdue Ojka, but the ALF arrive and save her and Mija, bringing them into their truck. Mundo and the officers chase after the truck, but they are taken out by a bag or marbles and Okja shooting poo at them.
Jay introduces himself to Mija with K translating for her. Jay explains the ALF's goal to protect animals from slaughter and expose the corporations exploiting them. He also tells Mija what the Mirando Corporation is really doing. They have been breeding other super pigs like Okja with the intent of distributing their flesh and organs for food. The ALF plan to have Okja go into the Mirando laboratories to expose the cruel conditions that the super pigs are subjected to, with a camera being placed under Okja's ear. Jay asks Mija for her consent in letting their plan go ahead. Mija wants to bring Okja back to the mountains, but K translates that she agrees to the mission.
In New York, Lucy and her crew view viral footage of Okja and Mija running through Seoul. Lucy fears that this will bring backlash to her company since there are images of Mirando associates forcefully carrying Mija away. Lucy's associate Frank Dawson (Giancarlo Esposito) helps her come up with an idea to have Mija and Okja reunited in New York City to bring back good publicity. Wilcox becomes upset when Lucy says she wants to make Mija the new face of the Mirando Corporation. She dismisses his complaints and has her team do damage control.
A drunken Wilcox goes into the lab and forces another super pig named Alphonso to mate with Okja. The ALF watch through Okja's camera with horror as Wilcox abuses the super pigs. They feel instant regret for sending Okja in there. K then admits that he lied about Mija letting them go through with their mission because he felt the mission needed to proceed as planned. Jay then starts viciously kicking and beating K for his deception, and he bans him from the ALF. Meanwhile, Wilcox starts angrily ranting to Okja about how Lucy humiliated him before extracting some of her meat. The meat is later tested by special tasters who declare it's the best meat they've ever tried.
Lucy's team preps Mija for her big reunion with Okja. Mija doesn't want to go through with everything that they have planned for her, but Lucy's assistant Jennifer (Shirley Henderson) shows Mija the kind of food Okja will become if Mija doesn't follow through. Mija goes to her room to find Jay there telling her not to look back during the big event, and that they will rescue Okja.
A parade is held in the city streets in honor of Okja being crowned the best super pig. The ALF are in disguise as civilians and participants to carry out their plan. Super pig meat is also being given out in the streets. Wilcox goes onstage to bring Lucy out for her to introduce Okja and Mija. Mija is shocked to find Okja with bloodshot eyes and cuts on her snout. The ALF then hack the screen to show the video of Wilcox abusing Okja and other horrifying images. The crowd turns against Lucy and Wilcox while Jay helps Mija get away. A response team, Black Chalk, then arrives to beat up the ALF. Jay tries to help Okja get away, but the team captures her.
Nancy Mirando steps in to clean up after Lucy. Nancy tells Frank about her plan to fix things for the public and to continue her distribution plan without a hitch, albeit at a reduced price for the meat.
K picks up Mija and Jay to rescue Okja for good in an attempt at redemption. They head to a plant where all the super pigs are being held for slaughter. The super pigs are being cattle-prodded as they are led to their fates. Mija desperately tries to rush to Okja. She makes it to the lab where the super pigs are killed and chopped up. Mija finds Okja being placed on the device that holds the super pigs down as they are executed. Before Okja is killed, Nancy comes to the lab with Frank and the other scientists. Jay and K are taken away by security guards. Mija pleads with Nancy to let her take Okja home, but she refuses. Mija then gives Nancy the golden pig from her grandfather to buy Okja. Nancy agrees and lets Okja go.
On their way out of the plant, Okja and Mija pass the other doomed super pigs. Two adult super pigs then push their piglet over the fence so that it can get away. Okja hides the piglet in her mouth to avoid detection.
Mija and Okja return to the mountains to be with her grandfather and the piglet, resuming their lives together in peace.
After the credits, Jay is being released from prison and is picked up by K. They hop on a bus with other ALF members, including a new member who worked for Mirando. Their plan is to hijack a meeting with Mirando shareholders. They don their ski masks to set their plan in motion.