John Reese, a former Green Beret and CIA field officer, was living as a vagrant in New York City after the death of the woman he loves. He is approached by Harold Finch, a reclusive billionaire computer genius who is living under an assumed identity. Finch explains that after September 11, 2001, he built a computer system for the government that uses information gleaned from omnipresent surveillance to predict future terrorist attacks.
However, Finch discovered that the computer was predicting ordinary crimes as well. The government is not interested in these results, but Finch is determined to stop the predicted crimes. 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, a corrupt officer whom Reese coerces into helping them, and Joss Carter, who is investigating Reese for his vigilante activities.