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 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.

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."

Sarah suspects that something fishy is going on at the medical clinic where she is being treated for insomnia. During her stay, she has flashbacks to a run-in she had with a man from the plant whom she thought she had already killed.

Sarah and John hit the road without Cameron and Derek to stay with Charley Dixon, where she reveals to Charley that her cancer may have emerged. Meanwhile, a computer worm infects John Henry.