Plo Koon was not a naturally nosy person. He didn't ask tons of questions or collect gossip. But for some reason, people just told him stuff. The rest of the Hufflepuff quidditch team--who'd nicknamed themselves "plo's bros" and "the wolfpack" (cause "badgers are stupid")--treated him like an older brother-slash-therapist, which was strange, since so many of his team mates were actually related, either as brothers or cousins. They had plenty of people to turn to, yet somehow he'd ended up as the confidant.
It applied to other people too. He'd been in his third year (he was year 7 now) when the Hogwarts house ghosts had responded to an innocent and mostly rhetorical question with the entirety of their story, stretched out over the year like a dramatic serial publication. He didn't know if any other students knew the whole story. Well, Obi-wan probably knew it, being such good friends with the Ravenclaw house ghost, but they were probably the only ones.
He wasn't sure though, if that was because it took so long to tell, or because they wanted to keep it a secret. So he was left with a sort of dilemma when Bly and Aayla asked what he knew about the story. He could easily tell an abridged version of the five house ghosts (that there were five, not four, was a very little known fact, and a story in and of itself), but decided to ask them all beforehand, just in case.
Most of them were in agreement that he could tell the story, except the Ravenclaw Ghost, who said she'd rather tell hers in her own time. That was fine with Plo. Her story was more distant from the others' anyway.
And so he began the story.
It started out as just Bly and Aayla sitting with him at the end of the great hall table, but as he warmed up and started using his storytelling voice, a few other people drifted by. He looked over and received nods from the ghosts. That was okay. And so he continued.
"I've told you the stories of the Gryffindor and Hufflepuff ghosts by themselves, but what is unknown to most of you is that these stories connect, drawn together by the ghost of Slytherin house.
"The story proper begins with a serious case of amnesia. Well, it begins long before that, but we start here. The Revans, conquerors of half the Wizarding world, were recovered from a shipwreck having no memory of who they were."
Two ghosts separated from the group on the other side of the room. They wore identical dark robes and masks and carried identical pairs of swords. The story's audience thought they were seeing double, but the ghosts of Slytherin tower reached up and removed their masks, revealing two different people, a young man and a young woman. Their face shape was similar, and it was clear they were siblings. Plo Koon continued his story. "What most of the world didn't know was that the great conqueror was in fact two people. This way they could create the illusion of even greater power, spreading their ambitious world vision even further, even as they worked to protect their identities."
"During their amnesia spell, this brother and sister gathered a crew of men and women and sailed the magical world, undoing the wrongs that they themselves had done. Their crew included Carth--" the Hufflepuff ghost stepped forward-- "who held and holds the sister's heart, Bastilla, who held the brother's heart, and Mission, their honorary daughter." The Gryffindor ghost joined them. "Together they regained their memories, defeated a great darkness, a former student of the Revans, and became protectors of the Wizarding world.
"The story of the Ravenclaw ghost, The Exile, as well as how they all came to be here at Hogwarts, are tales for another day."