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.

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.

Sarah and Cameron investigate a nuclear power plant; John grows less enthusiastic about academics but flourishes socially with the help of a new friend; Catherine Weaver gets another piece of the puzzle for her pet project.

Derek and Sarah must outwit Cromartie after he kidnaps Charley's wife, and they must weigh the consequences in rescuing her. Meanwhile, John finds himself unable to choose between Cameron and Riley.

While Sarah, John and Cameron track another name from their list, they accidentally cross paths with T-1001. Meanwhile, a woman who Derek once knew in the past surprises him by appearing in the present.

Cromartie kidnaps Sarah and races to Mexico to find John. When Derek, Cameron and Ellison discover what has happened, they come to their defense, which leads to one final deadly confrontation with Cromartie.

Terminators come after a family whose unborn daughter plays an important role in the war against the Machines, and Sarah, Cameron, and Derek try to protect them.

The Connors visit a town connected to the destroyed factory; Weaver sends a man into town in search of a survivor.

As the Connors prepare to move, they find out that Riley is dead, and Sarah begins to doubt Cameron's motives. Jesse flashes back to a submarine mission in the future, and John Henry plays hide and seek with Catherine Weaver's daughter.

Jesse's submarine mission in the future takes a fatal turn with unforeseen consequences. Back in the present, her plan to turn John against Cameron backfires when John discovers that Jesse--not Cameron--killed Riley and he makes a life-or-death decision.