"The Departed" is a remake of the 2002 Hong Kong film "Infernal Affairs." The movie follows the story of an undercover cop, Billy Costigan (Leonardo DiCaprio), who infiltrates a Boston crime syndicate, while a mobster, Colin Sullivan (Matt Damon), infiltrates the police department. As the story unfolds, both characters find themselves caught in a web of deception and loyalty, leading to a thrilling climax.