Hereditary

Miniatures artist Annie Graham lives in Utah with her psychiatrist husband Steve and their two children, 16-year-old son Peter and 13-year-old daughter Charlie. The family attends the funeral of Annie's estranged mother, Ellen. Annie is surprised by the number of mourners in attendance. After the funeral, Charlie becomes withdrawn and sullen; at school, she beheads a dead bird with scissors and pockets the head. At a bereavement support group, Annie reveals that she and her mother had a strained relationship, though Ellen largely raised Charlie. Meanwhile, Steve learns that Ellen's gravesite has been desecrated, a fact he keeps from Annie.
Peter is invited to a party, and Annie insists that Charlie accompany him. Left unattended, Charlie eats a piece of cake containing walnuts, triggering her severe nut allergy and sending her into anaphylactic shock. As Peter drives Charlie to the hospital, she leans out of the window to gasp for air. Peter swerves to avoid a dead deer in the road, and Charlie is decapitated by a telephone pole. In shock, Peter drives home and leaves Charlie's headless body in Annie's car, which she discovers the next morning.
Following Charlie's funeral, Peter becomes reclusive and guilt-stricken, Annie becomes bitter and resentful toward Peter, and Steve tries to mediate between them. Annie befriends fellow support group member Joan and reveals to her that, while sleepwalking, she once nearly set her children on fire. Joan encourages her to communicate with Charlie's spirit via séance. Annie reacts with skepticism, but Joan demonstrates her own ability to contact her deceased grandson Louie. Joan explains that all members of the family must be present during the séance.
That night, Annie dreams of Peter's head swarming with ants, as Charlie’s was after she died. During the dream, she confesses that her mother pressured her into giving birth to Peter but that she tried to miscarry. She wakes up, then wakes Peter and Steve to conduct the séance. Objects move and Annie speaks in Charlie's voice until Steve throws water on her. As supernatural forces start haunting Peter, Annie suspects Charlie's spirit has become vengeful and demonic. She sees threatening images manifest in Charlie's sketchbook, all involving Peter. When she throws the sketchbook into the fireplace, her clothes catch fire, only to stop burning when she extinguishes the fire.
Annie goes through Ellen's belongings and finds a photo album showing Ellen as "Queen Leigh", the leader of a coven, and Joan as one of her acolytes. Another book describes the demon king Paimon, who brings wealth and knowledge when summoned, but who prefers to inhabit a male host. In the attic, Annie finds Ellen's rotting, headless corpse and occult runes drawn in blood.
While Peter is at school, Joan appears across the street and attempts to expel his spirit from his body for Paimon. In class, Peter is taken over by an unseen force and slams his head against his desk, breaking his nose. Steve brings Peter home and Annie tells Steve about the body in the attic and about Charlie's sketchbook. She begs him to burn it, unable to take her own life. When he refuses, believing Annie has gone insane, she snatches the book and flings it into the fire, only for Steve to burst into flames. Annie watches in horror but is then possessed by the same force that possessed Peter.
As naked coven members gather in and around the house, Peter wakes after dark and finds his father's charred corpse. A possessed Annie pursues Peter through the house, and he takes refuge in the attic. Annie follows him, crawling on walls and floating in the air, then beheads herself with piano wire. Horrified, Peter jumps out of the attic window and hits the ground. A light enters his body, reviving him.
Now displaying Charlie's mannerisms, Peter follows Annie's floating corpse into Charlie's treehouse, where Joan and the other coven members, as well as the headless corpses of his mother and grandmother, are worshipping Charlie's crowned, severed head atop a mannequin. Joan removes the crown, places it on Peter's head, and proclaims him Paimon, telling him the coven has "corrected his female body" and given him his preferred male host. The coven hails Peter as King Paimon.