Spoilers for the secret event ahead, of course!
UPDATE: The mystery has been solved! Read through for instructions on how to complete the Secret Stones questline.
PRE-REQUISITES: In order to pick up this questline, you need to have done the previous "Secret Stone" quest chain. You or a friend will also need "Ashmar-aban", the gold necklace from completing the Howling Pits instance in the Iron Hills. This has a pre-requisite quest chain from Nain.
TO FIND THE STONES: Pick up the quest from Grimyr to the right of the steps up to the throne, inside Erebor. Complete the resulting instance, and talk to Thorin. Then you need to find Frethir in Moria, he can be found at the Bridge-shard in the Foundations of Stone. Next, you need to find the hidden lever on the path towards the Shadowed Cave, and enter the door that is revealed (make sure you are not mounted and have Frethir with you for the lever to appear). Have a look at the Terrainmap if you're struggling to find the path.
FIRST STONE: SOLVED!
Translation:
"Shield against
the howling winds"
Credit: Thoronlin, Altair6
Solution: Stormwall, Ered Mithrin. Hidden switch is at 38.1N 43.1W, the door is found at 38.6N, 43.8W.
Inside the chamber are two inscriptions, the first of which reads "The heir of iron holds the light in the darkness" (credit: Xaviere), and the second of which reads "Ashmaraban", the name of the necklace from the Howling Pit (credit: Lindalien). To get the necklace, you need to complete the "Howling Pit" instance in Jarnfast - the pre-requisite quest chain starts with "Beneath the Fold" from Nain. After you finish the instance, Nain has a new quest to turn the necklace into a wearable item. If you don't have the necklace, find someone else who does, and they will need to accompany you for the next step of the quest.
Down under the throne in Jarnfast, by the Howling Pits entrance, some "Hidden Runes" should become visible on the wall by the stairs. The runes say: "The symbols of his power adorn his crown", and "Aglâmbazari" (Glimmerdeep) (Credit: Duf of Ark and Silverrider). You now need to find a series of runes, each in order. You need to find each set of runes, one after the other, starting with the ones in Jarnfast, or you will not be able to progress the quest.
Rest of the runes (credit: Siddharta):
Glimmerdeep (landscape): 38.6N, 47.7W, behind the waterfall by the small bridge as you approach Glimmerdeep from the road
Thikiil Gundu (instance): 23.4N 135.9W, behind one of the statues in the entrance hall
Thikiil Gundu (instance): 24.2N, 135.4W, upper level of Afhan-binnin, on the back of the geode
Thikiil Gundu (instance): 25.0N 136.0W behind the central throne in Thikil-nesad
From here, travel to Zirakzigil and find the five levers scattered in the snow, by the dwarven statue-heads.
14.4N, 109.0W
14.8N 108.7W
15.0N 109.0W
15.1N 109.5W
14.0N 109.5W
Once you have the levers, head up the side of the mountain, past the Searcher's Eyrie. The Ancient Key can be found at 13.7N 110.0W. You can now unlock the door in the Stormwall chamber and claim the first stone!
SECOND STONE: SOLVED!
Transliteration:
"Kâm lagûrz
Flagzultaza
Skrizgurzu"
Credit: Mairie, Odobenus
Solution: Kam Lagurz in Lhingris, at 15.5N, 31.8E. The Emissary will charge you with finding the "Remnants of the Fallen Ones".
1st Remnant: The Mistress, Dar Narbugud
2nd Remnant: Behind the Blind One after defeating him, Dar Narbugud
3rd Remnant: 1st boss, Dark Delvings
4th Remnant: 2nd boss, Dark Delvings
5th Remnant: The Lost One, 16th Hall
6th Remnant: Twin Nameless Bosses, the Rift
7th Remnant: Thaurlach, the Rift (not necessary to kill the Ever-seer)
After you collect all the remnants, return to Kam Lagurz, and you can enter an instance with the Emissary. You need to speak some Words.
The Emissary tells us to "seek the Mighty Ones" before speaking the words. This could be talking about the Balrogs: when Thaurlach is defeated in the Rift, text pops up saying "The spirit of evil lingers still." Upon visiting Durin's Bane on Zirakzigil, there is text that says "The war with the Valar is eternal".
The remnants also each have a seemingly coded series of letters, each one different. This is possibly a cipher we need to decode. The codes are:
TPDnamqvtinadwmkxyyyfgvnjqfrty tl
hmqxwapxgvtsrnryepthxmqktVKDVJ ZSM
avwddmwfnrcwsyhwgrhevzbjdhwtlh jDJME
atkCPAPnwvtwwjknsqmomgup
avcjclluiUFEHMRZirwlitnvdnvnsj spwbmae
hmvdadvchvkelusnjUCCNGJnffoezb jcxtqobtnk
tpdypqSZwzxebbtxszqayzivfi
Inside the chamber there are also three scraps of paper with some Khuzdul translations, as follows:
The cipher has now been broken! The uncoded remnants read as follows:
ALL HAIL THE NAMELESS MOTHER
HER CHILDREN WHISPER THE NAME THROKHAR
ANXIOUSLY AWAITING THE CALL OF THEIR LORD
THE DAY OF HIS RETURN IS NEARING
THE SLUMBERING ONE SHALL HEAR OUR PLEA
AND ON THAT DARKEST DAY YOU WILL KNOW DESPAIR
HE WILL RISE FROM THE DEPTHS AND DEVOUR THE WORLD
Key decoding credits: Giseldah, Faratalath, Hephburz-2
Isolating the words capitalised in the code, we have the sentence "Hail Throkhar, Lord of the Darkest Depths".
Translating into Khuzdul: "Shamukh Uthrokhar, Uzbadu Bazari Uznanul".
Target the Emissary, and type /say: Shamukh Uthrokhar, Uzbadu Bazari Uznanul to claim the second stone! (Credit: cakeparsee)
THIRD STONE: SOLVED!
Translation:
"The hand fallen, the hand raised"
Credit: Gildoriel
Solution: Rockbelly Pit, Ered Luin, 15.7S, 102.3W. Go up a level for the switch, then the door is back downstairs. Inside the chamber we get a vision of a cave-troll breaking in and stealing the stone. The cave-troll can be found just to the left as you exit Thorin's Gate. We are informed that a Dourhand has taken the stone from the frozen cave-troll. The body of the Dourhand is at the Wardspire in North-Eastern Ered Luin. Next, we need to track down the goblins that killed the dwarf.
Rest of the locations, courtesy of Siddharta:
Goblins: Evendim, Southern Emyn Uial, 9.8S, 74.6W
Guaradan: Evendim, The Even-rills, Northern Emyn Uial 3.3S, 69.0W
Angmarim: Evendim, Candiach, Parth Aduial, 10.7S 64.8W
Ranger: Fields of Fornost, 12.3S 55.5W, and then in the pool next to him
Stone itself: Carn Dum (instance), inside the castle, several levels up towards Mordirith's throne room (through a door in the stairwell between boss 3 and 4, there's a dead Angmarim right outside).
FOURTH STONE: SOLVED!
Translation:
"Over the Land there lies a long shadow
Westward reaching wings of darkness"
Credit: Deorwyn, Gildoriel
Solution: The hidden switch is at Paths of the Dead, 45.8S 74.1W. The door is then at at 43.6S, 73.9W.
Entering through the door, we need to find a way to remove the runes inside the chamber. The next step is to speak to Marus in the Shadowed Refuge, 13.1S, 101.2W. We now have to find the original chisel. He also mentions a copper and obsidian rune-stone base, and a polished dwarrowgleam. The chisel can be found at 4.7S 106.0W, in the passageway north from the 21st Hall. You will also need a Polished Dwarrowgleam (Ironfold Jeweller), an Ironfold Chisel of Fire (Ironfold Metalsmith), and a Khazad-copper Obsidian Rune-stone (Supreme Jeweller, has to be the non-critted version). Once you have all these items you can talk to Marus, he will tell you how to remove the rune. The door can then be opened, revealing a second chamber behind where you can claim the fourth stone!
Once you have returned all the stones to the Crown Chamber, the mystery will be revealed! You can head up the path from the chamber to the Shadowed Cave entrance to complete the deed "Discovery: Askâd-mazal, the Chamber of Shadows".