EDIT:
This book is free, but google still insists on asking for payment details so it can charge you zero dollars. I can't fix this, sorry. But here's a link to the story available online anyways:
http://www.the-potions-masters-nephew.com/Chapters.htm
SeverelySnaped started writing and planning this indulgent fanfiction prior Order of the Phoenix. She enjoyed herself immensely.