In Hollywood, there is no such thing as a sure thing. A crime drama helmed by Martin Scorsese, the legendary director of classics such as Goodfellas, Casino and Mean Streets, comes pretty close, however.

After exploring historical epics in the highly lauded Gangs of New York and The Aviator, Scorsese returns to what he does best: crafting a complex tale of corrupt cops and undercover officers.

The Departed, a remake of a 2002 Hong Kong thriller called Infernal Affairs, follows Billy Costigan (Leonardo DiCaprio) and Colin Sullivan (Matt Damon), fellow officers in Boston’s state police department who get entangled with local crime boss Frank Costello (Jack Nicholson).

While Costigan infiltrates Costello’s organization to bring him down, Sullivan acts as his informant within the department. Soon, each side identifies a traitor in their midst, and Costigan and Sullivan are charged with identifying each other’s deceptive ways.

Since Costello lies at the heart of the story’s narrative, Nicholson’s portrayal fittingly anchors the picture. Having perfected the ability to play morally perverse individuals in films such as Batman, The Shining and A Few Good Men, Nicholson conveys Costello’s rage and desperation to hold onto his power, despite the fact that the authorities are closing in. Nicholson gives the character a modicum of humanity and a bizarre sense of humor, adding yet another memorable portrayal to his incomparable career.

Thankfully, amid an impressive ensemble that also includes Martin Sheen, Alec Baldwin and Mark Wahlberg, DiCaprio outshines everybody. After Oscar-worthy turns in Catch Me If You Can and The Aviator, he truly comes into his own in this film, at last shedding the pretty-boy image that has haunted his career since Titanic. With The Departed, DiCaprio firmly establishes himself as one of the most versatile and exciting actors of his generation. Now a frequent collaborator with Scorsese, he captures Costigan’s frustration and fear as he grapples with the psychological effects of his double life, drawing the audience in every second he’s on screen.

Although the film boasts a number of strong performances, The Departed‘s true strength is its gritty and often darkly humorous script from William Monahan (Kingdom of Heaven). Despite the necessary focus on the parallel journeys of Costigan and Sullivan, the film manages to give each character his own moment to shine, creating a textured and effective depiction of the tense inner workings of both the police and the mob. However, while The Departed is rife with stylized dialogue and unpredictable twists, the script leans toward campy on a few occasions, such as when Costello shouts, “This ain’t reality TV!” However, such moments are few and far between, never undermining the film’s tone or its central message.

Early on, Costello draws a comparison between cops and criminals, proclaiming, “When you’re facing a loaded gun, what’s the difference?” This intriguing notion effectively unifies the film, and Monahan’s script highlights the similarities between the police and those they pursue as Costigan and Sullivan, two men trapped by both sides of the law, struggle to survive.

A subplot involving the police psychiatrist (Vera Farmiga), who becomes involved with both men, serves to extend the parallels between them, bringing their conflict to a more personal level.

Through these vastly similar characters, The Departed explores the very nature of the law enforcement system, revealing the exceedingly thin line that separates cops from criminals. In the process, Scorsese presents a complex moral analysis of a world in which the corrupt and the righteous seem increasingly alike. In doing so, the filmmaker – who has yet to receive an Academy Award for Best Director – adds another instant classic to his admirable body of work.