The cat chasing the mouse is trope as old as stories are. It shows up all over film, from Tom and Jerry cartoons to Terminator. It is this trope that defines the plot of Martin Scorsese's 2006 crime masterpiece The Departed, which stars Matt Damon, Leonardo DiCaprio, and Jack Nicholson. In the film, set in Boston, Damon portrays Colin Sullivan, a man who is planted in the state police by mob boss Frank Costello (Nicholson) with the purpose of discovering the identities of any undercover police. Meanwhile, the state police have planted William Costigan (DiCaprio) within Costellos outfit to gather enough evidence for an indictment. Despite a 90 million dollar budget, Scorseses film doesnít feel lavish or grand. Instead, it achieves a perfectly pitched sense of claustrophobia, transporting the audience right into the tortured, paranoid minds of its characters.
On the surface, The Departed tells the story of two men hunting each other while trying to remain hidden. As they go deeper and deeper into their game of cat and mouse, everything becomes sinister in their eyes. Every funny glance or awkward interaction suddenly becomes life or death to them. Each knows that the other is only one false move away from discovery, and it tortures them mentally.
This dynamic is perfectly encapsulated in a scene about halfway through the film. Costigan tracks Sullivan to a theater, trying to get a glimpse of him without revealing his own identity. As Sullivan leaves the theater, Costigan follows. However, something, perhaps a 6th sense or premonition, tips off Sullivan that he is being followed, and Costigan starts chasing him through Chinatown, getting closer and closer until the men are within 30 feet of each other. Sullivan finally finds his opportunity and escapes without being seen, but the audience is left with the impression that the situation is a ticking time bomb, and when it goes off nobody will be left.
Underlying all the tension of the plot is theme of identity. The two main characters are essentially in a struggle for their identity. They spend so much time undercover that they begin to forget who they are, and where they are from. Sullivan begins to wonder if his assistance to Costello is worth the risk he is taking on. Ultimately, he only continues after Costello threatens him. Costigan, after Costello realizes that there is a mole in the mob, demands to be taken out of his undercover role and placed in witness protection. This leads to a pivotal scene wherein Costigans contacts in the police, Captain Queenan and Sergeant Dignam (Martin Sheen and Mark Wahlberg), refuse to allow Costigan to pull out. Dignam tells Costigan that he and Queenan are the only two people who know that Costigan isnít a criminal, and that he can be wiped off the face of the earth. It is after this that Costigan understands how truly alone he is, and begins to feel like he has lost his identity.
A story of such depth could not be executed without great performances from its actors, and that is exactly what Scorsese gets. Damon, known mostly for playing a good guy, excels in his role as a villain and provides an excellent foil to Nicholsons unhinged madness. DiCaprio, a longtime Scorsese collaborator, is given the perfect opportunity to display his trademark intensity, funneling it into the tortured psyche of Billy Costigan, in what is perhaps the best, and most nuanced, performance of his career. Scorsese displays a superb combination of respect to the genre and his own directorial magic, and the result is a film that will surely become embedded in the canon of great films about crime.