Harry is greeted at the Dursley's with aggression and sharp comments from Aunt Marge
Call to Adventure/Crossing the Threshold
After he leaves the Dursley's house Harry is found by Stan Shunpike, the Knight Bus driver. Stan takes him to Diagon Alley which is in the wizard world.
While staying in Diagon Alley Harry is reunited with his friends Ron and Hermoine
Once they're trapped underground Lupin and Sirius explain to Harry how Sirius was not guilty of his parent's death. Harry is at a crossroads and is not sure what to believe.
Now that the truth is out Sirius and Harry become familiar with each other and Harry gets to meet his godfather (the only relative that is nice to him). Sirius even sends Harry a Hogesmade permission letter.
Harry eventually has to go back to the Dursley's but he is still filled with excitement from his third year at Hogwarts.