What is the major plot of OOP?

[wpfositpoi <wpfositpoi@yahoo.com>]

No: HPFGUIDX 50097

Does anyone have any guesses on what the major plot of OOP will be?  

We've all speculated on smaller plot lines, character fates, etc. but 
there must be some story that sets all of that in motion.  It would 
introduce new aspects of the wizarding world, information on the past 
and be loaded with danger and, of course, a mystery.

In the first, it was the Sorcerer's Stone, then the Chamber of 
Secrets, then Sirius' escape, then the Triwizard Tournament.

This is probably impossible to figure out since JKR's imagination is 
so astounding but maybe someone out there has some ideas...

The only clue I can think of is that Harry's supposed to visit a 
place he's only heard of.  Azkaban, maybe?