"You know it?" Norrell prompts, immediately focused in on this -- ready to wring Childermass for information. "You have read it, then? And you believe there is nothing else to it? No hidden patterns, nothing woven into the writing? No spell upon it disguising the words?"

Already Norrell is quietly going through spells he knows that might fit such a thing, perhaps trying to think if Childermass would recognise any of them.