Percy is accused of the attempted murder of one major and one minor goddess and the fading of a minor goddess. He is sent to Tartarus but years later the gods realize their mistake and bring him back just in time for a war against a new villain. Only this time Percy isn't the same. Tartarus changed Percy and not in a good way.
This is an alternate ending of Harry Potter and the Prisoner of Azkaban. You may have already guessed the story line based off the title... but nevertheless, I hope you enjoy :)