Harry Potter and the Prisoner of Azkaban starts out – like so many of the Harry Potter books – with Harry at Number 4, Privet Drive, missing his friends and counting down the days until he can return to Hogwarts. When his repulsive Aunt Marge comes to visit, he loses his temper, inflates her like a balloon, and runs away from home. This is when we’re first introduced to the Knight Bus, which travels around Britain picking up stranded witches and wizards and taking them wherever they need to go. It’s also when we first meet Stan Shunpike, the Knight Bus conductor, who will later be arrested for a crime no one believes he’s guilty of, sent to Azkaban, and put under the Imperius curse by the Death Eaters when they escape en masse. How fitting that Stan, who becomes sort of a symbol of the Ministry’s corruption in Half-Blood Prince, is introduced at the same time that we get one of our early glimpses of their two-faced nature.
When Harry arrives at Diagon Alley, Cornelius Fudge is waiting for him. To Harry’s surprise, though, he’s not in any trouble for using magic on his aunt. Fudge just wants to make sure he’s safe and book him a room at the Leaky Cauldron. Harry, who has previously been warned that using magic outside of Hogwarts will get him expelled, is naturally suspicious, and he notices Fudge “suddenly looking awkward” when he brings it up. What he doesn’t realize yet, although he will, is that the Ministry has no desire to expel the famous Harry Potter while there’s a murderer on the loose who may be trying to kill him. That would be bad for their publicity. Harry will be safer at Hogwarts, so he’s spared from punishment for the time being.
It’s easy to overlook this, since, after all, it’s to Harry’s benefit. He won’t be so lucky a few years later, when he uses magic in a truly life-threatening situation and ends up facing a full-scale criminal trial for it. By that point, he’s making things difficult for the Ministry with his insistence that Voldemort’s back, and they’d like nothing more than an excuse to kick him out of the magical world. Fudge has a tendency to change the rules as it suits him, which Harry benefits from now but will eventually suffer from once he starts voicing truths the Ministry wants kept quiet.
There’s a lot about injustice in Prisoner of Azkaban. I actually wrote an essay on the topic in college – easiest, most enjoyable school paper I’ve ever written – and I’m sure some of that will come to the surface as I read through it again. By the end of the book, it’s more certain than ever that the Ministry of Magic is fallible and flawed, that their mistakes can ruin an innocent person’s life, and that they don’t always listen to reason. Already, in the earliest chapters, we have our first subtle hint at that unpleasant truth.