The Departed is a tense and bloody crime thriller, but what makes it brilliant is its doubling of characters, themes and symbols – not to mention the dizzying games it plays with betrayal. This deep-dive essay explains how the film (and its ending) works.

What is The Departed about?

Undercover cop Billy Costigan (Leonardo DiCaprio) is asked to infiltrate the Irish American mob in Boston, run by Frank Costello (Jack Nicholson). As a safety measure, only two other cops know Costigan’s true identity. Unknown to either of them, however, is that the Special Investigations (SI) unit is already home to one of Costello’s informers, Colin Sullivan (Matt Damon).

As each inside man struggles to discover the identity of the other, both risk being found out first. They’re right to worry: betrayal is the main theme of The Departed. Costigan is the police ‘rat’ in Costello’s mob, while Sullivan is the mob’s rat in the State police department – yet this is just the tip of the iceberg. All the characters sell each other out. No one can be trusted.

The double theory

Many narratives make use of opposites, i.e., characters and themes that are mirror images of each other. Think Jekyll and Hyde, Good Vs Evil, Cops & Robbers etc. The conflict between opposites is what makes drama (described in more detail in this essay about Jaws).

The Departed features many opposites and mirror images, but it goes one step further: the link between them is often almost too close to call.

Costigan and Sullivan is the most obvious example of this. They’re so similar they could be two sides of the same coin/ character. Their paths mirror each other almost identically, but from opposing positions (in the film, both literally follow each other around in almost exactly the same way).

Similarly, there are two gangs in South Boston – the Irish American mobsters, and the State Police. If they were merely opposites, it would be easy to differentiate between the two, yet both have their rats, corruption, loyalty and good intentions. Rather than being straight opposites, they’re almost the same entities seen from different angles.

“When I was your age, they would say we could become cops and criminals … when you’re facing a loaded gun, what’s the difference?”

~ Frank Costello

Costigan & Sullivan

Costigan and Sullivan are doubles. Both are young cops; both also work for the mob – but while Costigan does it to bring Costello to justice, Sullivan does it to protect him.

The two are even more similar at the start of the film. Both are hungry for recognition. Both have similar backgrounds, too – working class families, dead parents. Without knowing the finer details, they could pass for brothers (arguably they are brothers of fortune, with Costello being the father figure whose approval they both need).

“Do you want to be a cop, or do you want to appear to be a cop?”

~ Captain Queenan

Costigan and Sullivan are so similar as to be brothers, or perhaps mirror images of the same character. Where their paths split is at the recruitment interviews. “Do you want to be a cop, or do you want to appear to be a cop?” Captain Queenan asks Costigan. This is the killer question, and one that forces the separation.

Sullivan, who has grown up under Costello, knows how to lie (he even brags about this later in the movie). He knows how to appear to be a cop far better than Costigan does, despite being dirty – and uses his fancy apartment and ‘doctor’ girlfriend as part of the ruse.

While Sullivan is welcomed into the SI unit, Costigan (with his family’s criminal connections) is immediately shunted into undercover work. Queenan’s ‘prophesy’ comes true: Costigan becomes a real cop – one doing the work without the badge, gun and recognition.

Frank Costello: king rat

“I don’t wanna be a product of my environment. I want my environment to be a product of me.”

~ Frank Costello

Costello (Jack Nicholson) leads the Irish American mob. He’s not a sociopathic killer, but he is a very strategic one, seeing death is a necessary evil to his job and desires. “Non serviam”, he tells a young Sullivan – I will not serve – quoting Irish author James Joyce (though the quote is also attributed to Lucifer).

“The church wants you in your place. Kneel, stand. Kneel, Stand. … A man makes his own way. No one gives it to you. You have to take it.”

Frank Costello

Costello is an individualist, and is clearly anti-Church. His opposite is Captain Queenan (Martin Sheen), who leads the undercover police department, and is a known Catholic. Both are also father figures, yet while Queenan provokes loyalty and courage, Costello inspires fear and betrayal.

Between them they personify good and evil, but even here the boundaries are blurred. Costello quotes the devil’s words and will have nothing to do with God or the Church – yet it’s Queenan who, like the devil, ‘falls from heaven’ (literally, when he’s thrown from the roof).

Costello, though, is indisputably the rat king; an almost Shakespearean villain who creates a foul world in his own image. He nods at this when he misquotes Henry IV, Part 2: “Uneasy lies the head that wears a crown” (Costello actually says “Heavy lies the crown”).

If Costello sees himself as a Shakespearan king, he’s more like King Lear, the mad monarch who challenges his children to prove they love him. This is the tension that underpins The Departed: who ‘loves’ Costello more, and who will prove more faithful – Costigan or Sullivan?

It’s a futile game, because Costello is feeding information to the FBI himself. Faced with the ultimate double-cross, Sullivan calls the game out for the lie that it is, then implies that for all Costello’s sleeping around, he can’t have children. Again, there’s an element of doubling here: if we’re to believe Madolyn’s speech earlier in the film, Sullivan has this problem, too.

Madolyn Madden

Police psychiatrist Madden (Vera Farmiga) is another bridge that connects Costigan and Sullivan. Both men unwittingly share a ‘father’ in Costello, and a ‘wife’ in Madden.

Madden quite literally betrays Sullivan by cheating on him. It’s also fairly likely that her unborn child is Costigan’s but, because this detail is never spelled out, it’s another connection between the men – both ‘share’ a son.

This enforces the idea of doubling, i.e., of characters who reflect and repeat each other. Costigan and Sullivan are (thematically) the same person, so of course they share a father, wife and child. Madden even represents another instance of doubling in her name – Madolyn Madden (there’s also Costigan and Costello).

Because of the way the film ends, it’s not clear whether Madden also betrays Costigan. He leaves a file of evidence with her, to be opened if anything happens to him. If she does as asked, however, it would mean Sullivan would be arrested – but this isn’t how the film ends.

There is a suggestion that others finally get wise to Sullivan’s true nature, though. When Sullivan returns to his apartment after the funeral, even the old women avoid him, as though they know he’s dirty (notice too the carpets near the lift, which feature big red X patterns, as though X marks the spot). Shortly after that, Sullivan is dead.


Delahunt (Mark Rolston) may be another double for Costigan. He’s part of Costello’s mob, and notably plays a ‘guess the cop’ game which may well be a diversion.

According to the game, anyone who ignores the gang is a cop: that momentarily puts Costigan under the spotlight when he stumbles out of Costello’s bar, but also protects him (because he’s clearly far too interested in and involved with Costello).

After his death, TV reports claim Delahunt is the undercover cop – though Costello immediately calls this out as a police strategy. But there is a suggestion that Delahunt is an undercover cop: before he dies, he reveals that he knows Billy is the rat … and yet doesn’t give him away.

It’s easy to assume this is because he’s a second undercover cop. This would tally with the fact that Costello also puts two rats in the SI unit – a fact that even Sullivan is blind to until the end.


Foul-mouthed Dignam (Mark Wahlberg) is the ‘bad cop’ in a good cop, bad cop pairing with Captain Queenan (good cop, bad cop is another type of doubling; one intended to disorientate and catch out criminals). Queenan and Dignam are opposites in other ways, too: old Vs young, and soft-spoken Vs foul mouthed.

Dignam is also a double for Sullivan, with both men swearing allegiance to a father figure. For Sullivan, this is Costello; for Dignam, it’s Queenan. Dignam’s final act of vengeance is most likely powered by this relationship: it’s payback for patricide.

It’s a rat-eat-rat world

The Departed features one double cross after another. Ultimately, almost all the characters choose to wear masks of morality and loyalty in public, and pursue their own desires in private.

Moreover, in the world that Frank Costello has created – in which a man should take whatever he wants just because he can – there’s no escape from corruption and death, because everyone is primed to sell out his closest friends and family to get what he wants.

Given this, it’s no surprise that Costigan is killed just before he’s home free. This hits hard because Billy is the film’s most likeable or heroic character – and the only rat with a more noble end in mind (justice).

It also means the end of the film can be read in two ways. Firstly, Dignam executes Sullivan as a final payback (assuming he’s not a mole, too) – but presumably someone else will come after Dignam in turn. Some viewers may have hated the final shot that follows – of a rat walking across Sullivan’s balcony – yet it’s entirely in keeping with everything the film is about.

That closing shot is a reminder that, no matter how much the police or the mob attempt to clean up the city or take back control, there’s always one more rat out there.

Other films like The Departed:
  • Goodfellas and Casino (same director)
  • Infernal Affairs (the film The Departed was based on)
  • Reservoir Dogs (undercover cop)
  • Inception (Leonardo DiCaprio, ambiguous characters)

Picture credit: Frank Cone