Dolve Wayle map
1 - Bell
2 - Library
3 - Scrivener
4 - Candle/First Scaith
5 - Treasury
6 - Asters' chest
Follow Fitir and you will reach the room with the bell. You will need to protect your companion there, as the conducts the first part of the ritual.
The enemies won't be numerous, so you should handle them easily. The further road leads to the library.
As you're exploring the dungeons, Faitir will speak to you a couple times. The options you choose don't matter, but if you succeed is persuasion, you will learn your companion's true intentions faster.
Inside the library you will have to fight The Scrivener. It's just an ordinary skeleton with more life than usual, so defeat it quickly and protect Faitir as he's conducting the ritual. That way you will obtain the book.
The candle should be found in the next room, but it will turn out that one of Faitir's ancestors (First Scaith) took it. The thief can be found at the end of the tunnels. Speak to him and afterwards make a decision. You have two options: either kill Faitir and free his ancestors or defeat First Scaith and therefore help your companion in creating his private army.
Both fight are very similar, the only difference is that the First Scaith is aided by a group of skeletons. Regardless of your choice, in return for completing the mission you will receive a key to the nearby treasury and quite a lot of gold.