The Departed is Martin Scorsese’s most purely entertaining film of the past thirty years, which is a remarkable thing to say about a film this dark and this morally complex.

The film runs two plots simultaneously. Colin Sullivan (Matt Damon) has infiltrated the Massachusetts State Police on behalf of Irish crime boss Frank Costello (Jack Nicholson). Billy Costigan (Leonardo DiCaprio) has infiltrated Costello’s operation on behalf of the State Police. Both men know there is a mole on the other side. Neither knows the mole is the man in the mirror.

DiCaprio’s Billy is the film’s moral center, a man becoming someone he does not recognize because the institution that was supposed to protect him is incapable of doing so. Mark Wahlberg’s Dignam, abrasive and correct, is the film’s dark comic throughline.

Scorsese won the Oscar for Best Director for this film after years of inexplicable losses. No one objected.