Based on the Chinese gangster film of the same name Infernal Affairs, The Departed is set in Boston amid Irish-American mobsters and the cops who are their nemeses. Damon plays a gangster who has infiltrated the Boston police department as part of its cadet class and has been steadily rising through the ranks. DiCaprio plays a cop who's been deep undercover inside the mob. Each side works feverishly to flush the mole out, with deadly consequences.