This book makes several moral attacks on a legal system that is controlled by men like Lucius Malfoy who bully people until he gets his way. Due to liability and general xenophobia, Buckbeak is sentenced to execution for harming Malfoy, when every reader saw that Malfoy deserved to be scratched. Furthermore, once Black is caught, only Dumbledore believes that he is innocent, since nobody else cares to listen to a story supported by no evidence other than the words of Hermione and Harry. Cornelius Fudge even says at one point how bad losing track of Black will look for the Ministry of Magic. None of these are fair choices; they are just easy ones. A third choice involving this injustice is the assumption that Crookshanks killed Scabbers. This assumption was supported by evidence. In the cases of this story, the big people are framed, and yet the system won't bother to notice.
As shown by Lupin, who spends much of his time as a respectable professor, and then another part as a man-eating werewolf, we understand that everything is capable of having two sides. We see this again when Black is innocent, Hermione begins breaking rules, and Buckbeak's execution is reversed through a simple intrusion through time. Nothing in these stories is ever what it seems; everything stands in a position to surprise. In Harry Potter and the Prisoner of Azkaban, every story has two sides, and in a world where time may change, we have to believe that both of them can be true.
The reason Harry feels such personal hatred toward Black is the thought that he betrayed his best friend, James Potter. When it turns out that Pettigrew had done it instead, Lupin and Black turn snarling on him. "YOU SHOULD HAVE DIED!" Black yells at him, "DIED RATHER THAN BETRAY YOUR FRIENDS, AS WE WOULD HAVE DONE FOR YOU!" Harry finds himself facing Black in the first place because he went down the Whomping Willow to rescue Ron. One of the greatest and most repeated messages in this series is summed up by Hagrid's sobering advice to Harry and Ron in chapter fourteen: "I thought you two'd value yer friend more'n broomsticks or rats." Human relationships are the core of this book.
This novel plots one guilty creature after the next, only to wipe the slate clean and have someone else entirely prove to be the guilty figure causing distress at Hogwarts and in the Magical community at large. This motif of framing reminds us all that rarely are things as easy as they may appear. The wizard world is full of secrets and spells, and the false alarms in Harry's detective-work, the deeper he will have to dig and ultimately the wiser mature wizard he will become. This framing has a great deal to do with the earlier stated themes of unjust executions and the duality of things.
Almost all of the names in the Harry Potter series are significant. Sirius Black means, virtually, Black Dog; the name Remus Lupin has its origins in the Latin word wolf, and in a co-founder of Rome, Remus, who was suckled by a wolf. Take also, for example, Lucius Malfoy: the "mal" in numerous languages is rooted in the word "bad," and his first name, Lucius, is similar to Lucifer. Other names, like Dumbledore, have actual definitions—in this case, bumblebee in old English. One can liken this to Dumbledore, who is an ancient, wise wizard who works well and hard to sustain his community, the "hive" of Hogwarts. Professor Trelawney's first name is Sibyll, the ancient prophet of mythology. Furthermore, Padfoot, Moony, Wormtail, and Prongs all are indicative of the animal they represent.
The Quidditch game between Gryffindor and Slytherin represents each of the teams perfectly. The Slytherins attempt to injure Harry the week before the game, and when the day of the match arrives, they play a dirty game, knocking players from their broomsticks during the game, grabbing Gryffindor heads and broomsticks instead of simply the balls. The Slytherins fly poorly on very good broomsticks (bought by Malfoy's father so that Malfoy could play on the team). Futhermore, the Slytherin team is not integrated at all: they have a team of only boys, unlike the Gryffindor team, compiled of seven highly skilled, well-practiced girls and boys, flying on a full array of differently-priced broomsticks. Gryffindor plays fairly but retaliates hard, and Harry beats Malfoy to the Snitch, despite Malfoy's many efforts to halt Harry's progress.