"Remember this, Hobbes... what goes around, really goes around."
Police detective John Hobbes (Denzel Washington), gains notoriety for capturing wily serial killer Edgar Reese. Immediately after Reese is executed, Hobbes is plunged into the case of another murderer who seems to be copycatting Reese with scary attention to detail.However Hobbes's investigation soon leads him to discover that this is no mere copycat, as somehow Reese, or at least the evil that was inside him, has managed to survive the execution. Worse still, the demon is able to jump from one host to another, allowing it to kill at will and to terrorize Hobbes himself.As the battle of wits between good and evil becomes increasingly personal for Hobbes, he must turn to a theologian's theories on demonology as his only hope for defeating this ancient evil.
Brick Joke: A particularly dark example: "Forgot something, didn't you? At the beginning, I said I'd tell you about the time I almost died..."
Demonic Possession: The whole plot. Although not stated, it may be implied that believers can resist demonic possession (at least in most cases). It's said that strong-willed minds can resist demonic possession by touch, but not where the demon is loosed from their last host and within "five hundred cubits," or about a sixth of a mile.
Reeves/Azazel: I can't get inside you by touch, but even when I can, when I'm spirit, I won't. No. Better I get you for real. I'll fuck you up, down, left, right, coming, going. I'll get so close to you, so close it breaks you. And if that doesn't work, I have other ways. I have so many, many ways.
The End of the World as We Know It: AKA the "Fall of Babylon", stated to be the goal of all demons. By possessing humans they further evil in the world and get closer to it.
For the Evulz: What Azazel does to Hobbes is simply for fiendish sadism.
The Fourth Wall Will Not Protect You: Azazel is revealed to be the narrator of the story. Just before the movie ends, he tells the audience "See you around," and then we get an image of many people in New York walking in the streets, implying that Azazel is out there somewhere in our world again and has kept on possessing human beings.
He Who Must Not Be Seen: We never see Azazel's true form except the human host he possesses, though it may not even be visible to humans otherwise.
Inspector Javert: Lietutenant Stanton ends up becoming this when the evidence starts stacking up against Hobbes.
Ironic Echo: Hobbes throws Azazel's taunts right back in his face at the end of the movie, from "Open your eyes, look around sometimes," to smoking cigarettes laced with the poison he killed Hobbes' brother with, to singing "Time is on My Side".
Nigh Invulnerable: Azazel is a body-possession spirit, so attacking him directly will only kill the host. Hobbes figures out that he can be destroyed if there are no more humans in the vicinity for Azazel to possess if his current host wears out. What Hobbes didn't know is that Azazel can possess animals as well, and quickly takes over a cat at the end to escape.
Smug Snake: Azazel views Hobbes as more of a fun diversion than an actual threat, and seems to think that he's free to antagonize Hobbes as much as he wants because there's no way Hobbes would figure out what's going on, much less learn his weakness. He later realizes just how wrong he was when Hobbes almost kills him at the end.
Suicide by Cop: With a twist. Azazel possesses a random man on the street, who steals the gun hidden nearby and draws down on Hobbes, who is forced into killing him. The demon then possesses a nearby woman, explaining he can possess anyone within 500 cubits, or about a sixth of a mile, if suddenly loosed from his last host. Using this woman Azazel then smears Hobbes, saying he killed the last host without provocation, and the man had no reason to commit suicide by cop, plus the gun only had blanks in it, so the media buys it. Hobbes thus gets suspended, removing him from hunting down the demon.
Trauma Conga Line: Poor Hobbes: his whole life is systematically dismantled by Azazel. Apparently, this is what the demon likes to do to people who are particularly good, as he's been implied to have done it before, repeatedly.
Hobbes: You leave my family alone.
Azazel: But I'm still having fun! Aren't you still having fun?
Video Wills: A camera crew records Edgar Reeves before his execution. At one point in the footage, Reeves addresses Hobbes (who is watching it days after Reeves' death) directly.
"Can you imagine what it feels like to be alive for thousands of years, and then realize you're actually going to die, 'cause some self-righteous cop decided that he was going to save the fucking world?"
These tropes are inherent spoilers. Highlight at your own risk.
The Bad Guy Wins: Hobbes's only victories were that he prevented Azazel from killing his nephew and that he helped Gretta uncover some info that her allies could use in future battles with the demons. Outside of that, Azazel did exactly what he claimed he would do at the beginning of the movie.
Beware the Nice Ones: When Hobbes has to figure out which his co-workers Azazel is possessing, it turns out to be his likable partner Jonsey instead of his aloof, Jerk Ass superior officer.
Kill 'em All: By the end of the film, Hobbes himself, Jonesy and Stanton were dead.
Narrator All Along / Unreliable Narrator: Azazel, the demon possessing everyone, is actually the one talking and this is revealed at the end. He's using Hobbes' voice because this is the last human we see possessed.
Out-Gambitted: At the end, Hobbes lures two fellow cops, of which one is possessed by Azazel, into the woods to a secluded cabin. When the demon-possessed cop kills the other man, Hobbes shoots him, but Azazel is going to possess him next. Hobbes is smoking, and reveals his cigarettes are laced with cyanide. Since the demon is only destroyed if there are no hosts left to possess-which he can do even to normally resistant strong-willed people within about ten feet-the Xanatos Gambit appears to pay off, Azazel will have no place to go except in his dying body. However, the narrator is revealed to be Azazel himself, who reflects how at first he believed himself to be Out-Gambitted, but chuckles on seeing a cat near the cabin, saying "Ah, ah, you forgot something, didn't you? See you around, Hobbes." Crowd scenes are then shown, with the implication that Azazel possessed the cat, got it near someone else and hopped bodies from there, going free. Earlier, another cop had committed suicide at the cabin, implying his attempt to pull off the same Xanatos Gambit to similar results. The Rolling Stones' hit Sympathy For The Devil plays over the credits.
Villainous Breakdown: When he learns that Hobbes has trapped him to die, Azazel throws a pleasingly cathartic one when he starts cussing Hobbes out like a mad twelve-year-old and crawling around to find a new person to possess before his spirit dies.
Wrongly Accused: Azazel frames Hobbes (and in the past, Gretta's father) for his own crimes, and tricks him into killing his own host in broad daylight to get him charged with murder.