Date it hit shelves: July 8, 1999
What happens in the book: Harry ends another insufferable summer at the Dursleys and hears about an escaped murderer, Sirius Black, in the Muggle news. The wizarding world is also buzzing about the infamous Sirius, who had been held at Azkaban, a maximum-security prison for those who have committed severe crimes.
Mr. Weasley warns Harry that Sirius is after him. At Hogwarts, Dumbledore informs students that the school will be guarded by the dreaded Dementors, Azkaban guards who can suck the souls out of wizards.
Hermione exhibits strange behavior and seems to be enrolled in every single class, even those with conflicting times. Harry, Hermione and Ron enroll in Professor Trelawny's Divination class and Hagrid's Care of Magical Creatures class. Harry loses the first Quidditch match of the season when Dementors storm the field in search of Sirius.
When he learns that Sirius betrayed his parents and are to blame for their death, Harry vows to kill him. But Harry soon discovers that Peter Pettigrew once a good friend to Harry's parents and Sirius was in fact responsible for betraying the Potters' whereabouts to Voldemort. Sirius, it turns out, is actually Harry's godfather.
The Dementors find Sirius and are about to suck his soul when Hermione magically turns back time. Harry then conjures a powerful Patronus charm to save Sirius. Still a wanted wizard, Sirius goes into hiding, and Harry sadly returns to the Dursleys.
Sirius Black (Padfoot): A dog Animagus, an old friend of Harry's parents and Harry's legal guardian
Peter Pettigrew (Wormtail): Studied at Hogwarts with Black and the Potters. He is and has been loyal to Voldemort. As an Animagus, he changes into a rat. For 12 years, he resided as the Weasley's family pet
Remus Lupin (Moony): Also a friend and schoolmate of the Potters, Lupin is a full-fledged werewolf not an Animagus and professor of Defense Against the Dark Arts. He teaches Harry how to conjure the Patronus charm, which repels Dementors
Buckbeak: A hippogriff half-horse, half-bird in the care of Hagrid. Harry and Hermione save Buckbeak from the ax. Later, Buckbeak protects Harry and Hermione from Lupin when he turns into a werewolf. Buckbeak and Sirius fly away together
The Magic Gadgets:
Maurader's Map: Shows the Hogwarts grounds on a blank piece of parchment. When the map holder says, "I solemnly swear that I am up to no good," markings appear, showing everyone who is within the grounds. The map was created by Remus Lupin, Peter Pettigrew, Sirius Black and James Potter
Time-Turner: How Hermione travels back in time. She initially uses it to attend more classes but later needs it to go back in time and save Sirius and Hagrid's beloved Buckbeak
Sneakoscope: A spinning glass top that makes shrill noises when "deception" is nearby