在同一个地方待了两年后，莎拉·康纳觉得有必要换个环境，以免过于安逸。于是他们搬到了一个新的城市，约翰开始上学，并遇到了一个神秘的女孩。然而，危险突然降临，莎拉和约翰又陷入了为生存而斗争的困境之中。

Sarah与老友联系求助，John去见Sarah的前男友，Cameron结识新友。三人联手潜入抵抗组织安全屋，发现里面有人。与此同时，Agent Ellison发现Sarah还活着，而Sarah过去的一个危险人物也被唤醒。

Sarah visits Miles Dyson's widow to find the creator of Skynet. She leads her to a man named Andy Goode who used to work with Dyson and is building a chess-playing computer named "The Turk." John and Cameron try their best to fit in on their first day at a new high school.

Sarah reevaluates the capabilities of her friend Andy's computer after he enters it in a chess competition. During the competition Sarah meets a stranger with a history similar to hers. Meanwhile, Agent Ellison finds remnants from a past terminator battle.

While searching for some stolen cargo, John becomes separated from Sarah and Cameron. Meanwhile, Agent Ellison's murder investigation leads him to a surprising suspect.

Sarah breaks into Agent Ellison's apartment and discovers a file on her from her time at the mental hospital, leading her to Dr. Silberman, now a doomsday convert. Meanwhile Cameron signs up for a ballet class and John finds out how his mom escaped the mental hospital.

Sarah finds herself in a business transaction with a mysterious business man named Sarkissian, who claims to be in possession of the stolen Turk computer system and wants an exorbitant amount of money for it. Derek recalls his childhood before the so-called Judgement Day in 2011, when a nuclear war triggered by Skynet will destroy the world. Agent Ellison finally discovers that the terminator Cromartie is impersonating an FBI agent, and makes arrangements to apprehend him.

Derek finds the brain chip from Vick that Cameron had kept. John builds an interface for it and they discover a computerized traffic system is important to Skynet. Sarah decides it must be sabotaged. Meanwhile, Cromartie is checking through school records in search of John.

Flashing in and out of consciousness, fighting for his life Derek Reese recalls his future life battling the machines in 2027. Meanwhile, Sarah tries to explain the past to Charley.