Harry was a highly unusual boy in many ways.
Number of chapters: 22
Plot: The person responsible for the deaths of Harry's parents - the fearsome Sirius Black - escapes from the wizard prison of Azkaban and goes after Harry.
Sirius was Harry's godfather and his dad's best friend - as well as being pals with new DADA teacher Professor Lupin at school - and Harry finds out he betrayed his parents to Lord Voldemort.
In a shocking twist it is revealed that it wasn't Sirius after all that was the betrayer, it was another of Harry's dad's friends, Peter Pettigrew.
He can turn into a rat and has been pretending to be Ron's pet Scabbers for years.
But before anyone else finds out the truth Pettigrew escapes, leaving no witnesses to what has happened so Sirius has to escape on a condemned hippogriff called Buckbeak.
DADA teacher (and their fate): Remus Lupin. It's revealed that Lupin is a werewolf, and even though he is a brilliant teacher, he leaves the job.
Best Neville moment: Good old nutty Neville leaves the list of passwords lying around, enabling Sirius Black to break into the Gryffindor common room to get to Harry. Oops!
Last line: And grinning broadly at the look of horror on Uncle Vernon's face, Harry set off towards the station exit, Hedwig rattling along in front of him, for what looked like a much better summer than the last.