What do I know of the book?

Quote from DirtyDogP >>

What do I know of the book?

Hildigrim was restoring it from the fire damage, but it is finally in good enough shape to be read.

All of its pages were once blank. Only a handful of pages at the end of the book remain so. The rest are filled with handwriting that starts out crude but slowly becomes more elegant, hinting that it was produced by a person learning to write, who then practiced their writing by keeping a diary.

(Anything more will require actually reading it. Probably a discussion within the group, or a return to the Bistro would be in store. Or finding some comfortable place to sit down in the cemetery and having Drusk cast Light many times.)

Hildigrim closes the book after thumbing through it, looks up at his companions, and then focuses on Quillary. "Hainard's hairy toes," he says with a hushed, awe-filled voice. "Has that ever happened to you before?"

Quillary actually stops to think, her eyes look up at the night sky in thought. She stands like that for just long enough for it to become uncomfortable, then looks back at Hildi. "I have had many encounters with the near dead, and possession is not new to me, but having an object become possessed, well, it is known that the near dead can move objects, as a poltergeist does, but not this. You hold a life in your hands, Hildigrim, be gentle with her."

Jorin spits on the ground to ward off any lurking sorcery. 

Quillary, with her high Insight, interprets Jorin's spitting. "Yes, there is some evil at work, keeping this soul here. We must read this book, and see how we can help her move through the Veil." She looks around the City of the Dead. "We should return to the Road's End." And off she goes, without waiting for anyone else to agree.

Drusk (while stepping rapidly to keep up with Quillary, on the way back to the Bistro):
"What did you find, Hildigrim? I realize you want to read more before saying too much, but it seemed you had some insights after your brief perusal."

Taking Quillary's words very seriously, Hildigrim hands the book to Drusk. "Hold this for approximately five seconds," he says. After the half-orc takes the tome, the halfling bends down and begins haphazardly scooping the rest of his possessions back into his bag, all the while jabbering away concerning how all of the burned book's pages had been blank when he picked it up. "I chose it because the cover was so beautiful despite being burned," he admits. He continues, saying that thumbing through the book after the ghost "possessed" it revealed that only a few of the pages at the end of the book remain blank. "It reminds me of a child's diary," he says, strapping on the pack and holding his hands out for the book. He accepts it back from Drusk and then turns to follow Quillary. He continues, "The handwriting at the beginning looks as if the writer was just learning to write. A novice. Perhaps a child. Perhaps someone who learned to write as an adult. Either way, the hand is clumsy, unsure and inaccurate. But as the book progresses, the handwriting advances and becomes more steady, precise and elegant." As he has begun to actually read the book, even as they walk, he stops talking. It is only with gentle guiding by Drusk that the halfling even makes it back home safely. Once he's inside the downstairs, Hildi realizes where he is and excuses himself. He heads upstairs to his room to sit and absorb the book's contents.

Quillary, perhaps still unaware of societal norms, follows Hildi closely, and settles quietly in the corner of his room, watching solemnly but not interrupting. She is not concerned with Hildi, but rather is watching the book. Who knows why.

Hildi doesn't mind. He is used to ignoring everyone around him while he reads.

Jorin, unsure of how to deal with a ghost book, and concerned for his friends' safety in the face of such sorcery, will also follow Hildi to his room, where we stands sentinel nearby the halfling.

It is the next morning.
Everyone gets enough sleep to avoid exhaustion, but the time is otherwise spent by Hildigrim looking through the diary (and the others tending to him by bringing snacks and drinks).

Not everything can be read (still some fire damage to the book), but there is enough for Hildigrim to understand more.
How he chooses to inform the others is up to him.
(You can say that Hildigrim repeats everything in the hidden text, in which case everyone is allowed to read it.)

Diary info for Hilidigrim only:

Hildigrim will of course tell everyone everything he learns (everyone can read the spoiler). As a Waterdhavian, does Hildi have any separate knowledge of Yellowcrest Manor, the Yellowcrests, any of the offspring, Faerl, or even Vecken? And then, as a bibliophile, do either of the sketches mean anything to him? Feel free to roll for me if you want a roll or two.

As soon as Hildigrim utters the words "Sarah of Yellowcrest Manor", the ghost appears a short distance away from the group.
The anguished state of the young woman’s spirit is clear to anyone who sees her.
For a moment she clutches her hands in your direction... then recognizes your group and calms down (sightly).

(Everyone can read the "spoiler" in post 5240.)

As Hildigrim recounts what is in the diary, the ghost appears a bit flustered.
Drusk: "Sorry, Sarah. But in order to help you, we need to understand what happened, and that means reading your diary."
The ghost is embarrassed, but nods in agreement.
(At least this reaction distracts her from her normal anguish, even if it was for only a moment.)

Sarah is able to clarify a few points of Hildi's explanation, by making some throat noises or with gestures.
You realize that the reason why her ghost-mouth is a bloody mess (and why she can't speak) is due to her tongue being ripped out.

When Hildigrim reaches the last entry, Sarah is clearly angered. To emphasize that, she paces back and forth, punching the air in her frustration.

Hildigrim can do an Arcana check for the drawings of Lord Viallis’s book and the circle of runes.
But he can't do everything himself, in a timely manner.
Other members of the group could check recent Waterdeep records (History check) or gather information some other way.
Someone could spend time with Sarah, if you had specific questions and can interpret her gesture and throat noises.

"I feel bad for you, Sarah of Yellowcrest, a life spent as a servant and a death spent bound to this book.  How you must desire freedom," Jorin says.

"Show me, if you can, how you lost your tongue."

Quote from Guiltysparc >>

"I feel bad for you, Sarah of Yellowcrest, a life spent as a servant and a death spent bound to this book.  How you must desire freedom," Jorin says.

"Show me, if you can, how you lost your tongue."

Sarah points to the book.
When that doesn't work, she straightens up stiffly, and makes a pompous and sneering expression. After strutting like a peacock for a few steps, she then mimes grabbing something with one hand and hacking with a virtual dagger in the other. She then moves her hands to "draw" a circle in the air, then points to the book again.

Quillary watches this pantomime in horror. She comes over to Sarah like she might hug her, but doesn’t. Instead her eyes look angrily at the book, and she gnashes her teeth on Sarah’s behalf. 

"Are we in agreement that we must help Sarah?" Hildigrim pleads, looking at the others.

"Of course," Quillary replies with certainty.

Hildigrim, all serious, gives a decisive nod. "Let us name our assignments to get this done as quickly as possible. A great injustice has taken place. Furthermore, there is the potential that even more offenses have taken place since. Who knows what Lord Yellowcrest has been up to in the intervening years? I would like to research the drawings to find out what foul magic we might encounter." He looks at each of the others in turn to give them a chance to proclaim their intent.