The third Harry Potter book. Published in 1999. Often considered the point at which the series Grew the Beard.Sirius Black has escaped from Azkaban, the wizarding prison. In response, the Ministry of Magic sends Dementors, a race of dreadful creatures which either wear or are made of Black Cloaks, to guard Hogwarts and their Emotion Eating powers seem to affect Harry especially. Remus Lupin, meanwhile, makes his first appearance, taking on the dreaded Defense Against the Dark Arts post.The book's popularity may be partially due to the introductions of Sirius and Lupin, considered by some fans to be two of the coolest characters in the series. It also marks the point where the books started to become more serialized with each ending setting up the next one. It also has, quite possibly, the most complicated plot of the entire series, drawing in characters and events from all over the place; the Prisoner of Azkaban is obviously important, but the way he is important zig-zags several times over the course of the novel, and the same thing happens to a bunch of other characters. The end result is that, by the end of the novel, the story's landscape has irrevocably changed... and readers know that things are going to get really interesting from now on.As a side note, this is the only volume in the series where Lord Voldemort doesn't make an appearance.
Tropes exclusive to this book or at least especially prominent in it:
The Alcatraz: Azkaban, which was first mentioned in Book 2, becomes central to the plot in this one.
Awful Truth: Done twice, first with the story Harry overhears about how Sirius betrayed Harry's parents, and isn't just an insane criminal, then the real truth of Peter's even crueller betrayal. Whether the real truth is slightly better or slightly worse is debatable. On one hand, the traitor wasn't James's best friend, and said best friend is still alive. On the other hand Peter not only betrayed the Potters and murdered about a dozen innocent people, but also framed Sirius for his crimes, and got to live happily at the Weasleys for twelve years.
And don't call Hagrid pathetic in front of Hermione, unless you're looking for a slap in the face...
This book shows us how McGonagall reacts to someone deliberately pulling off foul play in Quidditch. TWICE.
And don't forget Harry's reaction to Aunt Marge's taunts.
Beware the Nice Ones: Remus Lupin. At the climax of the book when he and Sirius confront Peter with the evidence of his betrayal, Sirius asks him casually "Shall we kill him together?" and Remus simply answers "Yes, I think so".
Book Ends: The first and last chapters are called "Owl Post" and "Owl Post Again", respectively.
Burn the Witch!: Lampshaded: Harry's over-the-summer essay is about how pointless medieval witch burnings were, since the few times the victim was a wizard and not a poor ordinary Muggle, they could simply cast a flame-freezing charm and pretend to be suffering. They go on to mention that some witches and wizards allowed themselves to be caught and burned multiple times because they liked the fact that it felt like being tickled.
Care Bear Stare: Riddikulus (laugh!) has this effect on boggarts and Expecto Patronum (think happy thoughts!) on Dementors.
Cassandra Truth: Due to the convoluted truth of what really happened that night, Harry has a hard time convincing anybody. Also done comically, as Trelawney doesn't believe a prophecy that she herself just spoke.
Hey children did you enjoy this wonderful children's book full of wonderful awesome things for children well let me WRITE A BOOK BUILT ENTIRELY ON THE FEAR THAT A DERANGED, PSYCHOPATHIC MURDERER IS GOING TO EITHER KILL YOU IN YOUR SLEEP OR DESTROY YOU IN ANY SORT OF OPEN, PUBLIC SPACE.
If the climax hadn't occurred on a night with a full moon, Pettigrew would have been arrested and Sirius cleared, completely changing the arc of the next 4 books. Lupin probably would have also remained teacher, since Snape wouldn't have found Sirius while trying to bring Lupin his Wolfsbane potion and ultimately outed Lupin as a werewolf out of spite. This is especially funny when its revealed that Voldemort cursed the Defense Against Dark Arts position. So with this curse Voldemort was ultimately able to make a new body.
The only reason that Sirius even breaks out of Azkaban in the first place is that A) the Weasleys win the wizard lottery, B) this is apparently front-page news, C) Ron has Scabbers in the picture, and D) Cornelius Fudge just happens to be carrying that exact issue of The Daily Prophet when he visits Black's cell.
Harry just happens to get his hands on the Marauder's Map the very same year that one of its creators is teaching at Hogwarts. Not to mention the other two surviving creators also being around Hogwarts for that same year.
Covert Pervert: A History of Magic contains an amusing little anecdote: witches and wizards who were caught and burned at the stake cast a charm that would protect them from the fire while all they felt was a gentle tickling sensation. Wendelin the Weird enjoyed it so much that she allowed herself to be caught forty-seven times. Yep, she definitely enjoyed it.
Cruel Mercy: Harry asks Sirius and Lupin to spare Pettigrew's life, but not because he feels sorry for him; he just doesn't want them to become murderers. "He can go to Azkaban. If anyone deserves that place, he does."
Did You Just Flip Off Cthulhu?: Malfoy when he insults Buckbeak after Harry managed to tame and ride him. Needless to say, Buckbeak nearly tore Malfoy's arm off at the insult.
Lupin's werewolf condition and the wizarding community's reactions to it may be a social commentary on living with HIV.
A number of people (including the director of the movie) believed that Lupin was gay, so it could also be a metaphor for homosexuality; however, Rowling didn't write the character as gay (he married Tonks) and explicitly stated it was an HIV metaphor, so the signs don't fit quite as neatly.
Dragon Their Feet: the public's general opinion of Sirius Black; on the day after Voldemort's downfall, he was outed as a Death Eater, and went on to kill 13 people (12 Muggles, plus the wizard trying to apprehend him) before finally getting caught.
Evil Detecting Cat: Crookshanks. Justified in that Word Of God stated that Crookshanks is half-Kneazle, a magical cat-like animal that can tell if someone is untrustworthy.
Exactly What It Says on the Tin: Hagrid being Hagrid, he sees nothing wrong with assigning The Monster Book of Monsters. You have to tame the book before you can open it, and it is absolutely feral until you do.
Extreme Melee Revenge: When Harry first meets Sirius. Harry becomes so enraged that he forgets all about magic, forgets that Sirius is supposedly a powerful dark wizard trained by Voldemort himself, and forgets that Sirius is holding three wands. Harry charges Sirius down and nearly suffocates him.
Fake Kill Scare: At one point, they hear what they think is Buckbeak being executed. It turns out to be the executioner hitting the fence (in the movie: a pumpkin) with his axe after he finds out Buckbeak escaped.
Lupin teaching Harry's class how to deal with the boggart, a magical creature that is warded off with the combination of a spell and positive thoughts, foreshadowing him teaching Harry how to deal with Dementors.
Dumbledore mentioning to Harry that Trelawney's current record is having only two accurate prophecies made.
Harry's two Quidditch-match related dreams foreshadow two following books:
After the match against Ravenclaw, Harry dreams about following a silver shape through a forest, together with a galloping shape before coming to a clearing, foreshadows both Harry's own Patronus (a stag) and the scene in book seven where Harry follows Snape's Patronus (a doe) through a forest into a clearing.
Before the Quidditch match final, Harry dreams that the Slytherins came to the match riding dragons and that he has to dodge the dragons' fire on his broom. Cue book four, where Harry dodges a dragon on his broom in the first trial.
Game-Breaking Bug: The time-turner has the potential to be this for the entire series; much like the infamous The Lord of the Rings "why didn't they just use the eagles?" Plot Hole, many have questioned why somebody didn't just use a time-turner to stop all the bad stuff from ever happening. Somewhat justified in that Harry and Hermione don't actually change the past, but rather play out a Stable Time Loop. It's also mentioned that whenever someone does try to use one to make actual changes, it always goes very badly. Then all the time-turners get destroyed in the fifth book anyway.
Girls With Moustaches: Aunt Marge, in addition to being "large, beefy and purple-faced", has a small moustache.
A Glass in the Hand: After one jibe too many about his family, Harry makes the glass Marge is holding shatter. She assumes she was gripping it too hard, having done the same thing before.
Golden Mean Fallacy: Lupin explains that this is one of the advantages to tackling a boggart in groups. It might try and combine two peoples' fears and end up with something a lot less scary than either of them.
Gone Horribly Right: The purpose behind telling no-one that the secret keepers were switched was to make sure everyone went after Sirius Black. It worked.
I'm Standing Right Here: Aunt Marge makes several disparaging remarks about Harry and his parents while sitting at the same table as Harry. Harry spends most of the week trying very, very hard to think about something else.
Intellectual Animal: The Wolfsbane Potion sort of invokes this. When a werewolf drinks it, they are able to keep their mind human when transformed.
I Will Tear Your Arms Off: Hagrid says that if he had known Sirius' role in the Potters' death, he would have ripped him limb from limb. Hagrid is a half-giant, so a threat like this should be taken very seriously.
Kick the Dog: It's bad enough that Snape belittles and insults Neville in his own classes... but to have a small rant about how useless he is to another teacher is beyond cruel.
Know-Nothing Know-It-All: Snape has a moment of this when subbing for Lupin, claiming that the Kappa is more commonly found in Mongolia when it's actually Japanese. This gets followed up on in Fantastic Beasts: "Snape hasn't read this."
Laughing Mad: Offscreen, Sirius when he's arrested, which certainly doesn't help his case, even though The Reveal makes it obvious that it was due to heartbroken grief over James's death, the betrayal and the overwhelming irony of Peter's escape.
My Friends... and Zoidberg: Oliver Wood does it to himself, when he lists the members of the Quidditch team: "We've got three superb Chasers. We've got two unbeatable Beaters. And we've got a Seeker who has never failed to win us a match! (after long pause in which he realises he's forgotten someone) And me." This leads to a rather heart-warming moment when the rest of the team (including Fred and George) say they think he's a great Keeper.
Narm: In-universe example: the Riddikulus spell involves making your worst fear funny.
Overly-Long Scream: Ron uses up two whole lines of text to scream "AAAAAAAAAAAAAAAAAAAAAARRRRRRRRRGH! NOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!!!" after he wakes up to find Sirius Black standing over him with a knife.
Pet the Dog: In the film version. When Snape realizes there's an angry werewolf standing behind him, the first thing he does is to push three students he loathes behind himself to protect them.
Red Herring: Everyone believes that Sirius escaped Azkaban to kill Harry. His target was somebody else entirely.
Rushed Inverted Reading: When Hermione tells Professor McGonagall about Harry getting a Firebolt for Christmas and then the teacher goes to temporarily confiscate it so that it can be checked for jinxes/hexes (on the chance that Sirius Black sent it), Hermione hides her face behind a book that she holds upside down.
Aunt Marge, who is a professional dog breeder, refers to bitches when talking about Harry's mother.
Marge: You see it in dogs all the time, if there's something wrong with the bitch, there's something wrong with the pup.
She might be using "pup" as a double entendre as well. "Pup" can mean "a cheeky or arrogant boy or young man", which would fit Aunt Marge's view of Harry.
Sirius's Animagus form is as a black dog
Steven Ulysses Perhero: Many instances throughout the series, but this book introduces two particularly good examples: the werewolf Remus Lupin (Romulus and Remus were humans raised by wolves in Roman mythology; "lupine" means "wolf-like") and Sirius Black (Sirius is another name for the Dog Star; he transforms into a black dog).
Thirteen Is Unlucky: Sirius Black's last crime before being imprisoned: murder of 13 people. Fridge Brilliance kicks in when you think of the 13th "victim", actually Peter Pettigrew. Trelawney brings this up during the Christmas feast, claiming that "the first to rise will be the first to die". Harry and Ron get up at the same time.
Trelawney: My dears! Which of you left his seat first? Which? McGonagall: I doubt it will make much difference, unless a mad axe-man is waiting outside the doors to slaughter the first into the Entrance Hall.
Possible Foreshadowing/Fridge Brilliance, as you realize there were already thirteen people at the table because Peter Pettigrew disguised in Animagus form as Scabbers was in Ron's pocket, and Dumbledore stands up to greet Trelawney, making him the first to rise out of the thirteen.
Timey Wimey Ball: Largely averted, but there is one slight inconsistency. Hermione mentions that a lot of wizards who have abused time travel ended up "killing their past or future selves". The immutable time-line model used should logically preclude killing your past self (although not killing your future self). Perhaps Hermione is mistaken, or exaggerating. Or she's referring to the very first time someone goes back in time. Being a Stable Time Loop, there has to be a time where they actually go back. Then they panic and kill their past self, since there are two of that person in the time period. Someone else could easily see someone kill themselves, then see the killer vanish and report it.
You Dirty Rat: Peter's animagus form, full stop. One has to wonder how James, Sirius and Lupin didn't get suspicious about this, especially since Word Of God says that an animal form is automatic and cannot be chosen by the wizard.