Erick Obsidian is the Wheel Clan's local dwarven historian and asks you to find the lost burial ground of the Iron Clan and retrieve the Durin Stone. He gives you a schematic to build an iron key (this requires Mithril Ore (which can be bought at the Wheel Clan) and a Heartstone (which can be found around The Bedokaan Village)).
The Iron Key opens the Ancient Iron Chest in the Zoological Society headquarters in Tarant (it can also be opened using lockpicking and a fate point). This leads you to the place of lost voices. Travelling there, you find a strange device. You can place one of the drums into the device and a strange voice tells you to find Durin’s Truth.
While on another quest, you will find the book in Victor Misk’s house in a locked case. You can get the book by :
- Pick pocketing Mrs Misk for the key
- Using Prowling and lockpicking to open the case
- Buying it (I do not know the precise Charisma/Persuasion requirements, but I do know that if you have not been to the place of lost voices and used the cylinders activate the device she will not sell you the book regardless of how Charismatic/Persuasive you are.
- Breaking the window or door from across the street, or going inside, entering turnbased mode moving from inside to outside while having view thru broken window/open door into the case and casting unlock cantrip (make sure none of the guards is nearby)
Reading the book will mention a glass key and give you the approximate location of the Iron Clan.
You cannot open the door unless you have the key. The key can be found in the Panarri temple in Caladon (see part 13 on Main Quest) walkthrough. Once you have the key it is just a matter of inserting it in the lock and the door will open.
Here you find that Magnus belongs to the iron clan (assuming he is in the party at the time), in the second chamber you will find many automatons, the Durin Stone, some iron clan armor and the iron clan hammer. If Loghaire is in the party as well, Magnus and he will have a discussion about Magnus becoming the Iron Clan leader.
Returning the Durin Stone to Erick gives you some experience bonus.