- Madolyn and Costigan's relationship is genuinely sweet despite the circumstances. You can tell that if things were different, and Costigan was not in his situation that he would have liked to have been with her, and Madolyn for her part greatly misses Billy at the end, while, presumably pregnant with his child.
- Especially notable in Billy and Madolyn's relationship is how Billy compliments the childhood photo that Colin made her put away.
- Captain Oliver Queenan, who demonstrates a warm and fatherly compassion for all his underlings, not least Billy Costigan for whom he becomes a surrogate father figure.
- It comes to a head when he and Billy are trapped in a building with Costello's gang closing in: he decides to run interference with Costello's goons (a decision that ends up costing him his life) to keep them from finding out Billy's identity as the informant, buying him time to sneak down the fire escape. His last words to Billy sum it up perfectly: "I'll be fine. But if you get made, I can't protect you. Now, go!" When the goons, show up, he doesn't even draw his weapon - just asks if anyone has a light for his cigarette.
- He's an unrepentant asshole, but Dignam's devotion to the police force and the Captain is quite heartwarming.
- At one point he drops his abrasive act and tells Costigan without any malice and in complete sincerity that he's too smart to be a cop and would be better suited doing something else.
- Whether or not Delahunt was an undercover cop, his keeping Billy's secret after figuring out that he's one. Either he's protecting a fellow cop, or decides not to make his last act getting Billy murdered by the rest of the crew.
- It's a minor moment, but the mention of Billy's unseen cousin Stephanie says that she went to his fathers funeral despite how Billy's father had been estranged from the rest of his wife family (implicitly since before he and his wife even divorced).
- Ellerby being such a Benevolent Boss to Colin. Yeah, Horrible Judge of Character is in play given Colin's true loyalties but he's just so nice and encouraging to him (and from what he sees, it's justified).
Heartwarming / The Departed