Possessor

The film opens on Holly, a quiet hotel worker, calmly executing a brutal stabbing assassination of a businessman before being gunned down by police. The scene cuts to an unconscious woman, Tasya Vos, being disconnected from a neural-interface machine — Holly was her host. Tasya works for a secretive agency led by Girder. A surgically implanted device lets Tasya project her consciousness into an unwitting host body, perform a contract killing, and exit by forcing the host to commit suicide.

Back home, Tasya struggles to reintegrate. She rehearses mundane personal memories to anchor herself in her own identity. She is estranged from her husband Michael and their young son Ira; intrusive violent impulses bleed across into her domestic life, including a fleeting urge to kill Michael during a tender moment.

Girder assigns Tasya a high-paying job: Reid Parse wants his estranged father, data-mining mogul John Parse, and Reid's sister Ava killed so Reid can seize the company. The plan is to possess Ava's boyfriend Colin Tate — a working-class Brit working as a data harvester — and stage a domestic massacre. The implant is surgically planted in Colin's brain without his knowledge. Tasya links in.

As Colin she mimics his mannerisms, even sleeping with Ava to maintain cover. At the engagement event she brutally bludgeons Ava to death, then attacks John with a sadistic, prolonged knife assault rather than the clean kill Girder ordered. When she tries to force Colin's exit-suicide, his consciousness resists; the gun misfires and Colin survives with a head wound. Tasya is now trapped inside a host who is starting to realize something is wrong.

In the hospital and on the run, Colin and Tasya's identities blur. The film cuts between merged faces and overlapping voices. Colin pieces together that he has been hijacked. He uses drugs and paranoia to stay alert. The agency sends extraction operatives. Drawn by Tasya's lingering attachments, Colin goes to Michael's house. In a confused struggle, Michael is murdered in front of Ira — neither personality clearly in control at the moment of the killing.

The agency cleans up using their own tools. Girder possesses Ira and uses the boy's body to shoot Colin, killing the host and freeing Tasya's consciousness. Back at headquarters, Tasya is debriefed. Asked about her favorite childhood object — the memory anchor the company uses to confirm reintegration — she recalls a butterfly she once pinned in a glass case, but this time leaves out the guilt and sorrow she had attached to the memory in the opening. She has edited herself clean. The film closes on a small, satisfied smile — Tasya is now whatever the agency needed her to be, with no real self left for them to interrupt.