Chapter 3 - "The Knight Bus" - In which Harry tries to decide what to do, the Knight Bus arrives, and he asks to be taken to London. En route Harry learns about Sirius Black. He is met by Cornelius Fudge at Diagon Alley and installed in a room at the Leaky Cauldron.
The Trip to the Leaky Cauldron
[Harry] collapses in [Magnolia Crescent], certain that he's been expelled from [Hogwarts] for blowing up [Aunt Marge]. He begins plotting an escape and a life on the run when he feels, then sees, a large animal, and while backing away falls over.
The [Knight Bus] unexpectedly arrives with a bang, and [Harry] has to roll over to avoid being crushed. [Stan Shunpike] welcomes Harry aboard, and he quickly claims to be [Neville Longbottom] and pays his fare, as the bus takes off again.
As the [Knight Bus] rolls along, [Stan Shunpike] talks to [Harry] about [Sirius Black]'s crime and escape from [Azkaban].
[Harry] wonders about his punishment for blowing up [Aunt Marge], as the other passengers disembark the [Knight Bus] one by one. Finally, the bus arrives at the [Leaky Cauldron], and Harry gets off himself.
No sooner does [Harry] disembark from the [Knight Bus] than he runs into [Cornelius Fudge], the [Minister for Magic]. [Stan] and [Ernie] gawk at him once they learn his real identity, and [Fudge] takes [Harry] to a private room in the [Leaky Cauldron].
Harry Arrives at the Leaky Cauldron with a Bang
[Cornelius Fudge] kindly informs [Harry] that [Aunt Marge] has been put back to normal, and the [Dursleys] are willing to welcome him back, but Harry is confused that he isn't being punished for such a severe breach of wizarding law. Fudge then arranges for Harry to stay at the [Leaky Cauldron], elects not to sign his [Hogsmeade] form, and departs.
[Harry] lets [Tom] show him to his own room, where [Hedwig] is waiting for him, and falls asleep without even taking his glasses off.
Chapter 4 - "The Leaky Cauldron" - In which [Harry] enjoys his new-found freedom, purchases his school supplies, and meets with [Hermione] and [Ron]. [Hermione] buys [Crookshanks] after the cat takes after Ron's [Scabbers]. Back at the [Leaky Cauldron], [Harry] overhears Mr and Mrs Weasley talking about the danger he is in.
Glorious Days in Diagon Alley
[Harry] spends his days wandering [Diagon Alley], taking in the sights at the [Leaky Cauldron], hearing shoppers discuss [Sirius Black], getting homework help from [Florean Fortescue], eyeing the [Firebolt] in the window of [Quality Quidditch Supplies], and stocking up on supplies for the school year.