Parasite

Kim Ki-taek and Chung-sook live in a semi-basement flat (banjiha) in Seoul with their daughter Ki-jung and son Ki-woo. As the family has financial struggles and low-income jobs, family friend Min-hyuk gives them a scholar's rock meant to promise wealth. Leaving to study abroad, he suggests that Ki-woo lie about his qualifications to take over Min-hyuk's job as an English tutor for Da-hye, the daughter of the wealthy but naïve Park family. Min-hyuk trusts Ki-woo because he likes Da-hye and wants to ask her out when he returns. After Ki-jung helps forge a certificate for him, Ki-woo, posing as a Yonsei University student named "Kevin", goes to the Parks' home, where he is hired by the mother Mrs Park by the end of his first lesson.

The Kims' scheme is to secure jobs for each family member within the Park household while concealing their true identities. Ki-woo recommends "Jessica," actually Ki-jung, as an art therapist for the Parks' young son, Da-song, who has been traumatised after seeing a "ghost" in their kitchen. Ki-jung then frames Yoon, the Parks' chauffeur, by making it appear as though he had a sexual encounter in the car, leading to Ki-taek being hired as his replacement. The Kims exploit the peach allergy of the Parks' longtime housekeeper, Moon-gwang, to convince Mrs Park that Moon-gwang has tuberculosis, and Chung-sook is hired as her replacement. Meanwhile, Ki-woo begins a secret romantic relationship with Da-hye.

While the Parks are away on a camping trip, the Kims revel in the luxuries of the house when Moon-gwang suddenly appears at the door, claiming to have forgotten something in the basement. She goes through a hidden entrance to an underground bunker created by the house's architect and previous owner, who had kept its existence secret from the Parks. There, Moon-gwang's husband, Geun-sae, has been hiding from loan sharks and is revealed to be the "ghost" Da-song saw when Geun-sae was trying to leave the bunker to steal food. Moon-gwang begs Chung-sook to allow Geun-sae to continue living there in exchange for regular payments, but the three other Kims, who are eavesdropping, accidentally reveal their true identities. Moon-gwang films them and threatens to expose their deception to the Parks.

After the Parks call to inform the Kims that they are returning early due to a sudden severe rainstorm, the Kims quickly destroy all evidence of their ruse and subdue Moon-gwang and Geun-sae in the bunker, although Moon-gwang is injured during the struggle. The Kims manage to escape, but the torrential rain floods their flat with sewage water, forcing them to take shelter in a gymnasium alongside other displaced people.

The next day, Mrs Park organises an impromptu garden party for Da-song's birthday, with the elder Kims assisting while the younger Kims are invited as guests. Ki-woo enters the bunker with his scholar's rock, with intentions unknown. Moon-gwang is already dead from injuries sustained in the previous day's brawl; Geun-sae bludgeons Ki-woo with the rock, leaving him unconscious. Geun-sae then leaves the bunker and stabs Ki-jung with a kitchen knife in front of horrified party guests. Da-song faints upon seeing the "ghost" again. Chung-sook impales Geun-sae with a barbecue skewer after a struggle. While Ki-taek tends to Ki-jung, Mr Park orders him to drive Da-song to the hospital. Ki-taek, gradually enraged by the Parks' lack of empathy or awareness of their own privilege, stabs him with Geun-sae's knife and flees.

Weeks later, Ki-woo is recovering from brain surgery, and he and Chung-sook have been convicted of fraud and placed on probation. Ki-jung has died from her injuries, and Ki-taek – now a wanted fugitive – has disappeared. Geun-sae is presumed to have been a random homeless man, and the motives for the murders remain unsolved. Ki-woo spies on the Parks' former home, now owned by a foreign family, and notices a Morse code message in a light visible from outside. Ki-taek, hiding in the bunker, has buried Moon-gwang in the garden and sends daily messages, hoping Ki-woo will see them. Still living in a semi-basement flat with his mother, Ki-woo writes a letter to Ki-taek, vowing to earn enough money one day to buy the house and free him.