Plot

An agent works for a secretive organization that uses brain-implant technology to inhabit other people's bodies - ultimately driving them to commit assassinations for high-paying clients.

Tasya Vos is a corporate agent who uses brain-implant technology to inhabit other people's bodies, driving them to commit assassinations for the benefit of the company. While she has a special gift for the work, her experiences on these jobs have caused a dramatic change in her, and in her own life she struggles to suppress violent memories and urges. As her mental strain intensifies, she begins to lose control, and soon she finds herself trapped in the mind of a man whose identity threatens to destroy her own.

The assassin Tasya Vos works in an agency that uses brain-implant technology to commit murders while possessing other human bodies. Her chief Girder tells her that she is her best agent but would be better if she detached from her husband Michael Vos and her son Ira Vos. After Tasya last work, she has neurological problems and is tired, but she hides from Girder. Now, the agency is hired in a very lucrative contract to kill the millionaire John Parse and his daughter Ava Parse by Reid Parse that wants to inherit Parse's fortune. Tasya accepts the job knowing that she is fragile, and the assassination goes awry when her subject, Ava's lover and fiancé Colin Tate, resists and does not let her commit suicide when the job is finished.—Claudio Carvalho, Rio de Janeiro, Brazil

In an alternate 2008, Tasya Vos is an assassin who takes control of others' bodies to carry out her hits. Through an implant installed in the unwitting host's brain, Vos can use a special machine to insert her consciousness into their minds. She returns to her own body by forcing the host to commit suicide at the end of each job.

Due to the amount of time she spends imitating other people, Vos struggles with increasing detachment from her own identity and cannot fully separate her work from her interactions with her husband, Michael, and son, Ira. She "practices" assuming her normal persona the same way she practices impersonating her hosts. Thoughts of violence haunt her during ordinary domestic life such as when putting Ira to bed and having sex with Michael.

Vos's handler, retired assassin Girder, is critical of her desire to remain connected to her family and expresses the belief that Vos would be a better killer without personal attachments. In a debriefing session meant to reconnect her with her real identity, Vos sorts through a series of objects associated with personal memories and pauses on a butterfly that she pinned and framed as a child. She tells Girder she feels guilty for killing it.

Despite her fragile mental state and fatigue with her work, Vos agrees to perform a major hit on wealthy CEO John Parse and his daughter, Ava, by possessing Ava's fiancé, Colin Tate. The hit is only a partial success: Ava dies, but Parse survives. Vos attempts to flee the scene by forcing Tate to shoot himself but discovers she cannot make him pull the trigger.

Tate instead stabs himself in the skull in an act of rebellion. This damages the implant, and Vos discovers she cannot leave Tate's body or overpower his will. Tate, regaining control, does not know why he killed his girlfriend or why he has begun to experience false, fragmented memories of another person's - Vos's - life.

The traumatized and disoriented Tate flees from the crime scene to his friend Reeta's apartment. He kills Reeta while struggling with dissociative memories of the hit on Parse and Ava.

Eddie, another employee from Vos's company, arrives at the apartment to help her regain control and complete Tate's suicide. The attempt fails. Vos is still unable to make Tate kill himself.

Instead, Tate becomes aware of her presence inside his body; his consciousness overpowers hers in a psychic confrontation, giving him access to memories of her husband, child and home. He kills Eddie during their internal battle.

Tate then goes to Vos's home and holds her husband at gunpoint, demanding to know what she did to him. When Michael knocks the gun from Tate's hand, Tate kills him with a meat cleaver.

Moments later, Ira stabs Tate in the throat, finally killing him. Tate uses his last moments to fatally shoot Ira.

Vos returns to her own body and discovers Girder had taken control of Ira to end her struggle with Tate. With Ira and Michael both dead, she is now free of all human attachments, just like Girder wanted.

In another debriefing, Vos sorts through the same personal objects from the beginning of the film. She handles the butterfly again but does not express any guilt for killing it.