Here's not so much of a mystery, as an interesting tidbit:
In Dead Beat, Lash is able to recall the text of the Erlking book perfectly. But Harry never read it before Corpsetaker stole it. So one of her previous hosts must have read it. And Harry mentions that Wizard Peabody only published it about a century ago. That means Lasciel was running around sometime in the last 100 years. I wonder if we're going to see anything that she had a hand in?
And just to keep this as a mystery post, the question would be, who was Lasciel's last host, and who brought her down?
Not the case, in fact. Harry reads through the Earlking book the night of his first visit to B.O.B. (Bock Ordered Books), just before he falls asleep and has the dream about his dad. This was after Sheila introduced herself, but before he discovered who she was. In fact, later on (sitting at Murphy's kitchen table, talking about the possibility of summoning the Earlking using something in the book) there's this exchange between Harry and Butters:
"I have to figure out how to call up the Earlking," I said.
"Is that why everyone wanted that book?"
"Apparently."
"But you had it. Heck, you read it."
In fact, that's the same conversation where Butters' comment "It's too bad you don't have a photographic memory," just a few lines further on, leads Harry to realize that Sheila could help.
So no, she didn't necessarily
have to have read it before, but to keep the consideration alive, I'll point out that if she
hadn't previously read it through someone else's eyes, she was taking something of a risk in claiming to know it before Harry did. What if he hadn't?
LML
By the way, really cool idea, parthagenon!
