To take down South Boston's Irish Mafia, the police send in one of their own to infiltrate the underworld, not realizing the syndicate has done likewise. While an undercover cop curries favor with the mob kingpin, a career criminal rises through the police ranks. But both sides soon discover there's a mole among them.
Will Hunting has a genius-level IQ but chooses to work as a janitor at MIT. When he solves a difficult graduate-level math problem, his talents are discovered by Professor Gerald Lambeau, who decides to help the misguided youth reach his potential. When Will is arrested for attacking a police officer, Professor Lambeau makes a deal to get leniency for him if he will get treatment from therapist Sean Maguire.