[Locke.]

John Reese (Jim Caviezel), a former Green Beret and CIA field officer, is living as a derelict in New York City after an unspecified incident, and is presumed dead. He is approached by Harold Finch (Michael Emerson), a reclusive billionaire computer genius who is living under an assumed identity. Finch explains that after 9/11, he built a computer system for the government which uses information gleaned from omnipresent surveillance to predict future terrorist attacks. However, Finch discovered that the computer was predicting ordinary crimes as well. While the government was not interested in these results, Finch is determined to find a way to stop the predicted crimes. He hires Reese to conduct surveillance and intervene as needed, using his repertoire of skills gained in the military and CIA. Through a back door built into the system, Finch receives a Social Security number for someone who will be involved in an imminent crime, at which point he contacts Reese. Without knowing what the crime will be, when it will occur, or even if the person they were alerted to is a victim or perpetrator, Reese and Finch must try to stop the crime from occurring.

They are helped by NYPD Detectives Lionel Fusco (Kevin Chapman), a corrupt cop whom Reese coerces into helping them, and Joss Carter (Taraji P. Henson) who had originally been investigating Reese for his vigilante activities. Although Reese arranged for Carter and Fusco to be partners in the NYPD early in the series, for the entirety of the show's first season, neither was aware that the other was also working with Finch and Reese. Periodically, the team enlists the aid of Zoe Morgan (Paige Turco), a professional "fixer" who applies her skills to particularly difficult tasks. A major subplot concerns "HR", an organization of corrupt NYPD officers in league with budding mob boss Carl Elias (Enrico Colantoni). Led by several high-ranking officers, the members of HR work with Elias in an attempt to return New York to the old order, when the mob and police worked together. Elias, on the other hand, is merely using HR as a means to regain complete control of New York's organized crime. Despite his desire to be seen as a good cop, Reese forces Fusco to appear to be in league with HR, which allows him to keep tabs on the activities of both HR and Elias. A second major subplot is that of Root, a murderous female hacker who is determined to gain access to the Machine. Finch and Reese know little about Root and her objectives, but have begun to gather background information about her in an effort to stay a step ahead of her.