Following the events of "Terminator 2: Judgment Day," Sarah Connor (Linda Hamilton) felt that her nightmares of a machine-ravaged future world were long gone. Those feelings changed when on a beach in Guatemala in 1998, she watched in horror as her son John (Jude Collie) was murdered by a T-800 Terminator (Arnold Schwarzenegger), shattering her world once again.22 years later in Mexico, a couple watches as a glowing ball of light drops a naked woman not far from them. The young woman (named Grace (Mackenzie Davis)), seems to be unconscious, but before they can try and get her medical attention, local authorities arrive, making assumptions on the situation. As they try to apprehend Grace, she wakes up and in a surprising display of speed and skill, disables the officers! She then steals the clothes from the boyfriend, and his car before heading into the city.The next day, Dani Ramos (Natalia Reyes) wakes up her brother Diego (Diego Boneta), and greets her father Vicente (Enrique Arce), before she and Diego head off to work at a local automobile factory. Shortly after they leave, a glowing ball of light appears, and drops a new Terminator known as a REV-9 (Gabriel Luna) into the apartment complex where the Ramos family lives.When Dani and Diego arrive for work, they are surprised to see that a machine has taken over Diego's job. Dani goes to speak to the manager, showing her disgust that the factory is more concerned with automation than humanity. Dani tries to get the manager to consider keeping Diego instead of her, before returning to the factory floor. Heading towards Diego, she is surprised to see her father there, when suddenly, the sound of bullets are heard, and her father's body crumples to the floor as Grace attacks! Dani is shocked at the brutal attack on her father, before Grace grabs her, and Diego follows! As they run, the REV-9 morphs out of his Vicente disguise and gives chase. Grace attempts to fend off the attacks, but is helped when Diego drops a car engine on it!This buys the group some time to escape in a truck, but not before the REV-9 gives chase in a bigger truck, leading to a chase onto the nearby freeway. The chase leads to the truck the group is in to crash, with Diego being impaled by metal bars. Dani does not want to leave her brother, but is pulled away in time as the REV-9 crashes a vehicle into the truck, destroying it and Diego!The Terminator has now split into two formidable foes, one a metal endo-skeleton, and the other made of liquid metal. As Grace prepares for a last stand, an SUV skids to a stop, and out comes Sarah, wielding weaponry that incapacitates both of the REV-9's forms. As Sarah examines her handiwork, Grace and Dani jump into Sarah's SUV and drive off.Some distance away, Grace's body begins to shut down due to the energy she expended in trying to fend off the REV-9. Dani claims they should go to the Police, but Grace claims that will only lead to the REV-9 finding them faster. Dani then takes Grace to a pharmacy, where Grace grabs a number of medicines, before collapsing on the way out. However, Dani is surprised to find Sarah outside, having tracked them down! She explains that both Diego and Vicente are dead, before tossing Dani's phone out the window, claiming that it can aid the new Terminator in tracking them down.Taking them to a motel, Sarah gives the unconscious Grace the medicines she needs. When Grace awakes, she and Sarah come to blows, before explaining their stories. Sarah tells how she claimed to have stopped Skynet from creating Judgment Day but lost her son John, leading to her hunting down Terminators.Grace explains that she came from the year 2042, but instead of Skynet, the threat against humanity came from something called Legion. When Sarah claims she seems "almost human," Grace explains that she is human, but has just been enhanced to fight the machines.Leaving the motel, the group are unsure where to go. When Grace inquires how Sarah knew where to find them, she tells that it is from an unknown source. This source sends Sarah coordinates that show where a Terminator will show up, and each text includes the words, "For John." Grace manages to use her enhanced cybernetics to hack into the phone, and finds that the texts originate from Laredo, Texas. Dani directs them to head to her Uncle, who can get them across the border, feeling that whomever is sending the messages may be able to help them.Meanwhile, the REV-9 has infiltrated a surveillance system, and begins trying to track them down.The three women manage to hop aboard a train, to get to Dani's Uncle. On the trip, Dani asks Grace more about the future. Grace explains it took only three days to bring the world to it's knees. She lost her parents, but was saved by those fighting back against the machines, before volunteering to come back in time to protect Dani. Sarah then claims she knows why: with John now out of the picture, Dani is the "new Sarah," and will surely give birth to the savior of the future.The three soon meet Dani's uncle Felipe (Tristan Ulloa). As he and his associates help to get them across the border, the REV-9 is tracking their progress, and sends a false statement to US Border Patrol, claiming the group are hostiles. When they emerge from under a hole in the border wall, government agents are waiting for them. As they are taken away, the REV-9 attempts to down a drone and kill Dani, but not before Grace manages to save her, but ends up badly injured.After they are taken to a facility, the three women are split up. Dani is put in a cage with other detainees, while Sarah is detained elsewhere because of her criminal record. Medical staff are surprised at what they find when examining Grace, before she awakens and takes the group out. As Grace makes her way to rescue Dani she finds the REV-9 has infiltrated the facility!Grace manages to get Dani to a Helicopter, but Dani doesn't want to leave Sarah behind. Sarah manages to find the two and escape, but not before the REV-9 almost gets her! Grace chastises Dani for putting herself at risk, claiming she's "too important" to be doing that.The three fly to Laredo, where they find the source of Sarah's secret text messages...which are being sent to her by the same T-800 who killed John! Sarah's first impulse is to kill the thing, but not before Grace and Dani stop her. The T-800 claims that after he killed John, he remained without a purpose until he adapted to life as a human. Adopting the name of Carl, he formed a relationship with a woman and her son. This soon caused him to think of Sarah, and given he could sense when the time-flow was disrupted by Terminators being sent back in time, sent her the text messages to give her life purpose.Knowing the REV-9 is still after Dani, the group are unsure what to do to protect her. Dani however, claims she does not want to just be protected, and wants to fight. The group then go about trying to get her acclimated to using weapons. They also feel that the blast from an EMP could disable the REV-9, and Sarah reaches out to a Military contact.The group heads off to meet Sarah's contact, but the REV-9 is not far behind. Chasing them onto a military base, Sarah's contact manages to get them the EMP, and secures them transport on a heavy aircraft. It is here that Grace reveals the rest of her story, and why Dani is so important. It turns out that when Grace was a child, it was Dani who saved her, and united a number of humans in the resistance that fought back against the machines.The REV-9 manages to catch up with the group, and a fight ensues, wherein the plane is severely damaged, and the group plummets down near the raging waters of a hydro-electric plant.With their weaponry largely gone and the EMP having been damaged, the group attempt to fight against the REV-9 with all they have left. Carl and Grace manage to shove the REV-9 into the spinning blades of a nearby turbine, the friction causing it to explode in a massive fireball, severely damaging the facility, as well as Grace, Carl, and the REV-9.In the aftermath, the REV-9's liquid metal shell is deactivated, but it's endo-skeleton is still functional. Grace is also dying from her wounds, and begs Dani to use her internal power source, which should be enough to fry the REV-9. Though it pains Dani to do so, she retrieves the power source as Grace expires, before trying to take on the REV-9 herself. The battle appears to be lost, until Sarah yells for Carl to do something. He manages to take the power source, and pulls the REV-9 and himself down into the destroyed turbine core. At the bottom of the core, Grace's power source fries the REV9's circuits, and disintegrates the clothing and flesh on Carl. As he lays eyes one final time on Sarah and Dani watching him, he utters two words: "for John."Following these events, Sarah and Dani find Grace in the present day, happily playing among a number of other children. While things seem safe, it is still possible that more Terminators (powered by Legion) may still be sent back. This time, Dani intends to stay by Sarah's side, to help her...and hope that Judgment Day may never come for them.