Oh. [ Not the happiest of topics. But he's eager to help in some way, and it brings back...well, lots of memories of reading through his book the first time. ] The Dark One is...sort of this magical being. It's this darkness, dark magic, attached to a person, it makes them do really bad things, things they would never do otherwise. The only way to stop him is the Dark One's dagger. [ Which isn't ideal, because...his grandfather. :| ] Or...True Love's Kiss.

[ There's...more to say, but it's possibly heavy enough that he wants to give them a chance to respond before launching into the rest, and what he knows and remembers about his grandfather. ]