Harry Potter and The Ghost Re-Animated

Based roughly in Harry's fifth year at Hogwarts after his disciplinary hearing held in front of the entire Wizengamot. While soaking in the Prefect's tub, he strikes up a conversation with Moaning Myrtle, with surprising results, resulting in the canon timeline going astray as new allies come to help out at Hogwarts, bringing their own variety of chaos and revelations.