The Demigods at Hogwarts

Percy wonders how he got here.
All he knew was that the gods apparently owed Hecate a favor in return for being their spy against Kronos, and that translated to the demigods owing her a favor.
Now, he and the rest of his friends from both camps had to pose as the Salem Institute of magic, travel all the way to Britain, and participate in some kind of battle royal between other magic schools, just so they could fight a megalomaniac who wished to take over the world and end a war that should have finished years ago if wizards weren't so idiotic and prejudiced.