The Medium (2021)

A documentary crew travels to the Isan region of Thailand to interview Nim, a medium who claims to be possessed by the spirit of Ba Yan, a local deity. She was chosen to be Ba Yan's host after her sister, Noi, refused to accept the role and converted to Christianity.

Nim attends the funeral of Noi's husband, Wiroj, who died of cancer, and reveals that misfortune has befallen the men in his family. Wiroj's father, a factory owner, killed himself after being caught committing insurance fraud. Wiroj's son, Mac, died in a traffic accident. Noi is left with her daughter, Mink, and they live with Manit (Nim and Noi's brother) and his family.

Mink starts behaving strangely and exhibiting multiple personalities, including those of an attention-seeking child, an old man, a drunkard, and a prostitute. She also hears voices in her head, has nightmares, and experiences abdominal pain and vaginal bleeding. She is fired from her job after her boss discovers that she has been having sex with different men at her workplace. Nim initially believes that these are signs that Ba Yan has selected Mink to be the next host, but Noi refuses to give her consent for a ceremony to transfer Ba Yan's spirit from Nim to Mink.

Nim later learns that Mink had committed incest with Mac, who had actually hanged himself, and believes that Mac's ghost is haunting Mink. After Mink attempts suicide, Noi thinks Ba Yan is punishing her for her earlier refusal to become Ba Yan's host by making her daughter suffer, so she arranges for another medium to conduct a ceremony to transfer Ba Yan's spirit to Mink. This is done without Nim's knowledge or approval. The ceremony fails; Mink becomes possessed by multiple spirits and attacks her mother before running away. In desperation, Nim advises Noi to open her heart to Ba Yan and seek forgiveness. Noi agrees and follows Nim to Ba Yan's shrine to pray.

A month later, Mink is found in a delirious state in the ruins of her grandfather's factory. Seeing Mink's condition, Nim visits Ba Yan's shrine once again, only to discover that the deity's statue has been decapitated. Nim confronts Mink and asks who they are, but Mink merely strips and taunts Nim, saying that Noi did everything she could to force Nim to become a shaman instead of her, including putting talismans in her shoes and making her wear her clothes.

Nim brings Mink to see Santi, a more powerful medium, who says that Mink has been possessed by numerous evil spirits. Mink's paternal ancestors had been cursed for committing many wicked deeds, hence the misfortunes that have befallen her family over the generations. The failed transference ceremony worsened Mink's condition by making her more vulnerable to possession by any spirit. Nim, along with Santi and his students, prepares for an elaborate ritual to exorcise Mink. In the days leading up to the ritual, Mink wreaks havoc at home by briefly abducting Manit's son, boiling the family's dog alive and eating it, among other things. Nim dies in her sleep the day before the ritual.

During the ritual, which is conducted at the ruined factory, Noi offers her body as a vessel to attract all the evil spirits haunting Mink so that Santi can exorcise her, trap all the spirits in a container, and bury it deep underground. Meanwhile, the possessed Mink has been locked in her room, and the door is sealed with paper charms; Manit's wife and others keep watch to ensure that she stays inside until the ritual is complete. Halfway through the ritual, Manit's wife hears her son's cries coming from Mink's room and thinks that Mink has kidnapped him again. She enters the room, only to be stabbed to death by Mink. All hell breaks loose when the evil spirits possess everyone involved in the ritual, causing them to fight and kill themselves or each other.

Meanwhile, Mink kills everyone at home and goes to the factory, where she encounters her mother and a few survivors. Now possessed by evil spirits, Noi momentarily claims to be Ba Yan's host when she chants a prayer while touching her daughter's head, attempting to exorcise her. This seems to work until she is distracted when Mink apparently returns to normal and calls her "Mother". Mink takes the opportunity to burn her mother alive, while the survivors are eventually overwhelmed by the possessed.

A mid-credits scene shows Nim undergoing a crisis of faith one day before her death. Before breaking down in tears, she wonders whether she has truly been possessed by Ba Yan or if she has been imagining it all along.