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.

The Connors find themselves on high alert and in odd company after their house is robbed. A Terminator terrorizes Ellison, while another gets dangerously close to John Connor. Derek and Jesse continue to get reacquainted.

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.

Sarah's quest to find the meaning behind the "three dots" leads to a technology firm seeking an advanced microchip. Meanwhile, Jesse comes clean to Derek about her mission and Weaver makes an important introduction.

Cameron learns that a terminator was accidentally sent back to 1920s Los Angeles, and she tries to find out what happened to him. Meanwhile, John has a run-in with a group of punks while taking Riley home from a party.

Sarah turns to a UFO convention for answers about the "three dots," more details about Riley's mission are revealed, and Ellison begins working with Catherine Weaver's AI prototype, "John Henry."

While fighting to stay alive, Sarah is guided by the image of John's father. Weaver's attempt to protect John Henry has deadly consequences.

While Derek does surveillance on a lawyer he suspects may be connected to Skynet, Sarah and Cameron begin to have doubts about Riley.

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.