In El Paso, Texas, various members of an organization that guards undocumented migrants have been murdered. Detective Garnica informs Tania, one of these activists that she must protect herself and her assigned migrant, a teenage girl called Alba from these attacks. Alba is one day away from doing her American citizenship test. Garnica tells them that he’ll be in their neighborhood bar that evening, and leaves them with a special dispatch line to contact the police force assigned to protect them.
That night, someone begins to harass them from outside by flashing lights into their bedrooms and throw rocks at the house. They don’t see anyone. But an intruder breaks into the house. Alba and Tania hide in the bathroom and make a plan, before he breaks the door down. They call the cops but nobody comes. They attack the intruder with the shower curtain and toilet lid, briefly weakening him. They escape to the backyard where the intruder attacks them, but they manage to hold him down.
The intruder reveals his name: Kenneth, and he’s there to kill them both, all part of a white supremacist militia’s plan to hunt undocumented immigrants and those protecting them. They decide to make a negotiation: He will leave peacefully with one of them, not killing anyone. Tania offers herself to be taken by him. But as they’re leaving, Tania notices a red laser dot on Alba. There is a sniper. Tania covers Alba and both re-enter the house barricading it against the intruders.
Kenneth realizes he has left his knife inside with his fingerprints. He attempts to break in again and succeeds, but Alba and Tania catch him and leave him unconscious. They negotiate with Banner, the sniper: He’ll be allowed to take Kenneth and his knife, and no one will know about the incident. Banner accepts but Kenneth wakes up, trying to call off a deal. This causes a fight between the two men that ends with Kenneth murdering Banner. Tania implores Alba to take the opportunity of the fight so she can escape. Alba escapes and goes to the coffee shop where Detective Garnica is supposed to be. Finding him there, she alerts him to the home invasion.
Tania tries to fight off with Kenneth, but just as he’s about to kill her, Detective Garnica shoots him dead. All seems well until the detective reveals he’s been behind the operation as well. Tania kills him and tells Alba that she’ll run away. Alba passes her exam and becomes a citizen. Months later, Alba now lives alone in El Paso. During an outing in the park, she sees Tania from afar, watching over her.