"The Departed" is set in South Boston where the state police force is waging an all-out war to take down the city's top organized crime ring. The key is to end the reign of powerful mob boss Frank Costello from the inside. A young rookie, Billy Costigan is assigned to infiltrate Costello's mob. While Billy is working to gain Costello's trust, another young cop, Colin Sullivan is among a handful of elite officers whose mission is to bring Costello down. But what his superiors don't know is that Colin is working for Costello, keeping the crime boss one step ahead of the police.