It could start out were Ambrose says that Malistaire was after ancient artifacts that contained massive powers that would enable him to take over the spiral yadda yadda yadda.
So then you defeat some evil boss guy and get a book reveling the location of Hogwarts, were the artifacts are hidden. Like the Scorers stone and all that.
I don't have all the details figured out, but i think it would be cool to walk around Hogwarts, meet Harry Potter. Maybe even fight Voldemort!
