POSSESSION

Mark is a spy who returns home to West Berlin after a mission to discover that his wife, Anna, is seeing another man and wants to separate. Mark turns over their apartment and custody of their young son, Bob, to Anna. After a long drinking spree, Mark returns to find Bob alone and unkempt. He resolves to be Bob's primary caregiver and unsuccessfully pressures Anna to end her extramarital relationship with a phone call. Anna leaves during the night, allegedly to stay with her friend Margie.

Mark meets Bob's teacher, Helen, who inexplicably looks identical to Anna except for her hair and green eyes. Mark visits and attacks Anna's lover, Heinrich, who beats him down. Mark returns home to find Anna with Bob, and the couple argues, culminating in Mark repeatedly striking Anna; she then leaves.

Mark hires a detective to tail Anna. He later interrogates Anna about their relationship, and she cuts her own neck with an electric knife. Mark treats her wound and cuts his arm with the knife. The detective follows Anna to her derelict apartment and calls to inform Mark of the address. The detective finds a bizarre creature in the bathroom, and Anna kills him. Mark withholds Anna's address from Heinrich. Helen helps Mark care for Bob and reveals that Bob has begun to experience sleep terrors. After putting Bob to bed, Helen and Mark have sex.

Anna kills Zimmermann, the detective's work superior and romantic partner, after he finds the tentacled creature and the detective's body in her apartment. Heinrich leaves Mark a film reel that shows Anna hurting one of her ballet students by holding her in a difficult pose to test her willpower; Anna tells Heinrich that their relationship is similar. Further footage shows Anna describing a conflict between Faith and Chance, as well as the pain that her affair will cause to Mark.

Anna returns and tells Mark that she is caring for her Faith in her apartment after violently miscarrying it in the subway while he was gone. After Anna leaves, Mark reveals her address to Heinrich. Anna shows Heinrich the creature and dismembered corpses before stabbing him. Heinrich flees and calls Mark to arrange a meeting at a bar. Mark discovers the body parts at Anna's apartment, but Anna and the creature are gone. Mark meets Heinrich, kills him in the bar's toilet, and stages it as an accidental death. He sets Anna's apartment on fire and rides home on Heinrich's motorbike. He discovers that Anna has stolen Zimmerman's car and killed Margie, who saw the creature. Mark and Anna have sex. Anna takes the creature to Margie's place. Mark takes Bob to Helen's apartment, then drives to Margie's place, where he witnesses Anna having sex with the creature. Mark visits Heinrich's mother, who kills herself by overdosing on pills.

Mark resists pressure from two former associates to rejoin their mission. He later finds them approaching Margie's place with a police officer. Mark forces a taxi driver to ram the police car as a distraction to allow Anna to escape in Zimmermann's car, though Margie's body is dislodged from the trunk, and Mark is badly wounded in a shootout and motorbike accident while fleeing. He enters a building and climbs its staircase until he collapses. He is found by Anna and the creature, now a fully formed doppelgänger of Mark with green irises. Mark raises his gun to shoot it, but a hail of bullets from the police below strikes him and Anna down. Mark and Anna share a final kiss before Anna kills herself with his gun, and Mark jumps to his death. The doppelgänger climbs the stairs and mysteriously compels a woman to fire on the police so that he can escape.

Helen is babysitting Bob when her doorbell rings. Bob implores her not to open the door, but Helen ignores him. Bob races to the bathroom and drowns himself in the bath. The sounds of sirens, planes, and explosions fill the air outside. The silhouette of Mark's doppelgänger is seen through the frosted glass door as Helen stares straight ahead, her green eyes shining.

Mark and Anna's violent descent culminates in multiple deaths, Anna's union with a monstrous entity, and Mark's confrontation with authorities as chaos engulfs their lives.

The film concludes with its characters consumed by the forces—psychological, supernatural, and institutional—that have haunted them throughout. As Anna and Mark spiral out of control, the boundaries between self and other, love and destruction, are shattered, leaving the audience with a sense of dread and existential uncertainty. Possession’s climax cements its reputation as a feverish meditation on obsession, identity, and the monstrous within.