Online:Ancestral Adversity

Quick Walkthrough
# Enter Dreloth Ancestral Tomb and find Narsis Dren.
# Follow Narsis Dren through the tomb and defeat the monster within.
# Meet Narsis Dren at Veloth Ancestral Tomb on the west coast of Vvardenfell.
# Solve the ancestor puzzle.
# Delve the tomb and defeat Matriarch Rathila.
# Settle the matter with Narsis Dren.
# Speak with Elfbetta the Shy outside of the tomb.

Detailed Walkthrough
At a camp outside the Dreloth Ancestral Tomb, speak to Elfbetta the Shy. She'll express concern for her employer, Narsis Dren, as he has failed to return from exploring inside the tomb.

After agreeing to help look for the wayward treasure hunter, enter the tomb. Dren will assume you're his new assistant and will make remarks about a "dangerous creature". Questioning Dren will reveal he is looking to raid the tomb for all its worth, as apparently the tomb sits above two other long forgotten structures that have not been touched for centuries. But before continuing, he'll ask you to dispatch the "creature" plaguing the adjacent room. Once you've dealt with that problem, Dren will lead you through the tomb.

Enter the Ancestor Prayer Room and talk to Dren. After some consternation and doubt that he has the right tomb (''"Oh, that's a V not a D"''), he presses a button and disappears behind a door. Follow Dren and you'll come across a Grievous Twilight. He'll ask you to defeat the beast and meet Elfbetta outside once you're done (and promptly disappears).

Defeat the Grievous Twilight, raid the urns, and speak to Elfbetta. She'll tell you to meet Dren at the Veloth tomb on the west coast.

Once you reach the Veloth Ancestral Tomb, Elfbetta once again will ask you to look for Dren. Entering the tomb will reveal that Dren has got himself locked behind a door. He'll explain how he didn't realize it was a trap and asks you to try to unlock the door with the plates along the wall that have Daedric runes inscribed on them. He offers guidance by trying something that's "divisible by three". Looking at the wall, select the third from the left. Once you find the right panel, he'll emerge.

Continue to follow Dren and he'll eventually lead you to a room where he asks you to look for a secret entrance. Read the harp pedestal and then the book Honored Ancestors, then take the four relics from the center of the room and place the appropriate relics to the correct tombs.

Llirala = mirror 
Ondre = arrow 
Valyne = goblet 
Elms = grain 

Play the harp to reveal the hidden door and follow Dren through. 

Continue to follow Dren, looting and slaying, until he once again becomes trapped behind another locked door. He'll ask you to press some more plates to release him. If you threaten to leave him in there, he'll note that he found a key to the next section of the tomb. Release him and follow him through yet another door.

In the next room, watch for traps and defeat the beasts. Solve the floor tile puzzle and open the gate:
On the left and right walls you see Daedric letters. Step on the corresponding floor tiles in the same order. If you do it right each floor tile will glow as you step on it. Starting with the second tile from the left, it is then forward, right, forward, forward, right, forward (spelling the word "VBERMAC"). Continue to follow Dren as he picks up a gold skull with emerald eyes and "ignore any odd sounds".

Next is an underground cavern. Dren is impressed with the well-preserved corpses, until they start to attack. At the end defeat the boss Matriarch Rathila and follow Dren into the next section.

In the last room, Dren is disappointed to find a bunch of broken crates and an old well. You can tell him to embellish the adventure in his next book or trick him and tell him the treasure is down the old well. Once he gets to the edge, you can push him in for his just rewards.

Go back outside and speak to Elfbetta. If you sent Dren to the depths, you can tell her he's "well" and is exploring "one more hole", at which point she'll give you your reward.

Notes
Speaking to Elfbetta before Dren, she'll tell you she discovered a scroll about the tomb.  Dren will first tell you he found it, but when called on it, will clarify that he translated it.
Pressing the wrong plates when Dren is trapped will cause him to be mildly tortured, if you so wish.
Bugs
The quest is notoriously buggy.
 
Workaround: Leaving and re-entering the area sometimes helps, though you may have to resort to abandoning the quest and starting over.

Gallery
 

Quest Stages