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.
Martin Scorsese's The Departed is a licensed remake of Andrew Lau and Alan Mak's 2002 Hong Kong masterpiece Infernal Affairs. Scorsese and screenwriter William Monahan transplanted Lau's structural DNA directly: the mole in the police force, the undercover cop in the mob, the paranoia of doubled identities, the identical fate awaiting both. Rather than conceal this, Scorsese made it explicit—a Hong Kong film given Irish-American geography and American scale. Both versions are essential to understanding modern Hollywood narrative architecture.