Of evil grandfathers and godly boyfriends

Percy's life was going a lot better than it could've been after the second war. He was going to university, he had a wonderful boyfriend, and his mother and step-father had just welcomed the cutest girl into the world. That was, until Gandalf, a werewolf, a hellhound (?), a carrot, and a 15 year-old showed up at his apartment to tell him he had yet another evil grandfather.