The Departed Ending Explained: A Tale Of Two Rats

It's been fifteen years since Martin Scorsese blew us all away with the ending of "The Departed," a twisted tale about double lives, secret identities, organized crime, and police corruption. The crime drama was a remake of the 2002 Hong Kong thriller "Infernal Affairs," modified for American audiences with a Boston setting. It was also loosely based on the real-life Winter Hill Gang, and Jack Nicholson's character Frank Costello is based on Irish-American gangster Whitey Bulger. (Bulger was most recently portrayed onscreen by Johnny Depp in the mostly-forgettable 2015 film "Black Mass.")

In "The Departed," Billy Costigan (Leonardo DiCaprio) is an undercover cop in South Boston. He's assigned to infiltrate the mob syndicate run by Costello, and he quickly gains Costello's trust. Meanwhile, Colin Sullivan (Matt Damon), a hardened criminal with ties to Costello's organization, begins rising through the ranks as a police officer, working as an informant for the mob. Both are consumed by their double lives, and each is constantly in danger of being exposed. The only way to survive is to expose the other man, but both are in so deep that it could be impossible. 

In a film with this many twists, turns, and secrets, it's easy to get a little lost. So let's look at the end of "The Departed" and untangle the movie's threads one at a time. Major spoilers ahead, naturally.

At the height of Costigan and Sullivan trying to figure out one another's identities, Sullivan discovers that Costello is an FBI informant. Sullivan fears that Costello might reveal his own shady dealings, so he arranges a raid with Costigan's help to take Costello down for good. After a shootout, Sullivan finds a wounded Costello and shoots him repeatedly. It's both an act of protecting himself and a bit of revenge for Costello's betrayal by going to the FBI. 

Following Costello's death, Costigan receives a mysterious tape. On it are recordings of Sullivan and Costello, proving that Sullivan is Costello's mole within the Boston police. He creates copies of the recordings and sends some to Sullivan in a manila envelope, to let him know that his secret is no longer safe. 

One major complication in both Costigan and Sullivan's lives is their relationship with therapist Madolyn (Vera Farmiga). She initially has a romance with Sullivan, though it begins to fall apart as he grows more involved with his duplicity on the force. When she starts falling for one of her patients, the undercover Costigan, it complicates things further: both men are bitter enemies but have no idea as to their respective identities. 

Madolyn lives with Sullivan, and when she sees the manila envelope Costigan left for him, she opens it. She listens to the recordings and realizes that Sullivan is an informant for the mob. Sullivan walks in on her listening to the recordings and tries to reassure her to no avail. He then calls Costigan who informs him that he has more copies of the recordings and will reveal Sullivan's duplicity to the police unless Sullivan helps him get his civilian identity back. He's essentially stuck undercover because of Costello's death and Sullivan's hand in it. 

The two meet up to exchange the recordings and paperwork to ensure Costello's return to a normal life, but things go haywire. They're ambushed by another officer, Barrigan (James Badge Dale), who kills Costigan and reveals to Sullivan that he was also a mole working for Costello. Sullivan kills Barrigan and concocts a wild story about how Barrigan was the mole all along and that Costigan figured him out. He nominates Costigan for a posthumous award and seems to think that's the end of it.

The final sequence of "The Departed" shows Sullivan returning home from the grocery store, only to be ambushed by his police superior, Dignam (Mark Wahlberg). Dignam, who had served as Costigan's handler during his undercover operation, shoots Sullivan dead and then leaves. 

The most likely explanation for Dignam's actions is that Madolyn gave him the tapes of Sullivan and Costello after Costigan's death. He knows that not only is Sullivan the rat, but he's responsible for Costigan's death. Dignam doesn't want to take Sullivan to internal affairs; he wants him dead. It's revenge, plain and simple. 

The other possible explanation is that Dignam was working with the FBI, and he knew about Sullivan's betrayal long before things got murderous. In this case, his motivations for killing Sullivan are based less on revenge and more on covering up the FBI's knowledge of corruption within the South Boston police force. Either way, shooting Sullivan is the best thing Marky Mark's ever done onscreen.

The very last shot of "The Departed" has inspired no shortage of controversy. After Sullivan drops dead and Dignam walks away, the camera pans up to a rat crawling across the patio railing. Some fans found the metaphor too on-the-nose, and one guy went as far as creating a crowdfunding campaign to digitally remove the rat. 

A "rat" is slang for someone who betrays the trust and comradery of whatever organization they've sworn themselves to. In "The Departed," Costigan was a rat to the mob because he was informing the police. Sullivan was a rat to the South Boston police, giving vital information to Costello, who was also a rat to the mob through his reports to the FBI. 

The literal rat is just a little joke — look ma, a rat in a story about rats! Maybe Scorsese just wanted us to end the movie with a little chuckle, because otherwise, that ending is tremendously bleak.