In 2029, John Connor, leader of the human resistance, leads the war against the machines. At the Los Angeles offensive, John's fears of the unknown future begin to emerge when John is notified by his army unit, Tech-Com, that Skynet will attack him from two fronts, past and future, and will ultimately change warfare forever.
On the verge of winning the war against Skynet, Connor sends his trusted lieutenant Kyle Reese back through time to save his mother's life and ensure his own existence. However, Kyle finds the original past changed. In this timeline, a Terminator was sent back in time to kill Sarah Connor as a child and so the Resistance sent their own cyborg back in time to protect her. After the assassin killed her parents, the reprogrammed T-800 raised and trained her to face her destiny, which she adamantly tries to reject.
Now, faced with a new mission, Kyle, Sarah and the old ally Terminator, have to escape the T-800, the recent T-1000, and as well as a new and horrific enemy: John Connor himself, who has been converted into a nanotechnological human-cyborg hybrid, the T-3000, all sent by Skynet to kill them. With John Connor compromised, they must find a way to prevent Judgment Day from happening.