New York City cabbie Jerry Fletcher (Mel Gibson) is an expert on paranoid conspiracy theories. He is also infatuated with government lawyer Alice Sutton (Julia Roberts), who permits his attention because he once rescued her from a mugging. However, when Jerry is captured and put through psychotic tests by Dr. Jonas (Patrick Stewart), he realizes there is an actual conspiracy. After escaping, Jerry enlists Alice's help, but she wonders whether he has uncovered a real threat or is just insane.