Of Heirs and Changes

Harry Potter's life changes drastically in his third year, with Sirius being released from of Azkaban. Not only that, but Lord Voldemort has regained his sanity and his soul, and has decided to take up the mantle of Slytherin lordship. Harry's in for a lot of changes, but is he ready? More importantly, is the world ready for the sweeping change to come? AU, obviously.