Skyrim:Vald's Debt

Quick Walkthrough
# Talk to Maven Black-Briar about erasing Vald's debt.
# Find the Quill of Gemination in Lake Honrich.
# Bring the quill to Maven.
# Give the note to Vald.

Detailed Walkthrough
To Catch a Thief
With hard evidence in hand, you and Karliah inform Brynjolf of Mercer Frey's nefarious deeds. Brynjolf decides that more intelligence is needed on Mercer's plans and asks you break into Riftweald Manor to see what you can find out—with impunity.  

The Watchdog
Ask Brynjolf about Riftweald Manor and he will mention a "trained watchdog" guarding the house; a man named Vald that Mercer is extorting. Brynjolf suggests you speak to Vex for more on Vald.  Vex has a few choice words about Vald, but will also tell you that he is working for Mercer Frey because of a debt he owes to Maven Black-Briar.  Clearing the debt is suggested as one way to get Vald to stop guarding Mercer's house.

The Queen Bee and the Quill
To learn the details of the debt, track down Maven, who can typically be found at The Bee and Barb. She tells you that years ago she commissioned a unique quill from Winterhold. Vald was to deliver the quill to her, but he lost it at the bottom of Lake Honrich, outside of Riften. thumb|The location of the quill shown on the local map 

From Riften Stables, head southwest until you reach the edge of the lake. Ahead, you should see a large ship docked at Riften. Swim towards the westernmost end of that ship and look west across the lake towards Goldenglow Estate to see a similar ship docked there. Halfway to the other boat, the prow of Vald's sunken rowboat can be found at the bottom of the lake. For reference, a small island to the north will mark the halfway point. You'll see half a boat prow sticking out of the ground and the quill is located in Vald's Strongbox (leveled lock)  . Pick it, take the quill and a leveled amount of gold, then head back to find Maven. She'll hand you a note to take to Vald.

Clearing the way
Head to the back gate of Riftweald Manor and wait there until Vald comes to talk to you. Inform him that you have erased his debt, and he will want to do you a good turn as well, giving you the key to the Manor and opening the back gate for you.

Notes
The quill does not spawn until you have spoken to Maven about it, so you cannot skip this step.
It's possible to keep the quill for yourself. To do this, talk to Maven to get the quill to spawn, go and obtain the quill, then go to Vald and intimidate/bribe him to let you pass. The miscellaneous quest will disappear from your quest log and the quill will no longer be marked as a quest item and is free to be dropped/deposited. This was done with the Unofficial Skyrim Patch installed. Results may vary.

Bugs
 
If the undelivered letter bothers you, it seems you can place it on owned bookshelves. You can also leave it on his corpse.
The dialogue option to tell Vald his debt is gone appears as soon as you've picked up the quill. Turning it in to Maven is therefore optional.
 
You can also try using Pacify if he becomes hostile and you don't wish to kill him.
Alternatively, approach him with your weapon out and when he attacks go into the console, click him, type  , exit the console, then sheathe your weapon.

Quest Stages