Skyrim:Dampened Spirits

Quick Walkthrough
#Speak to Maven Black-Briar.
#Meet Mallus Maccius at The Bannered Mare.
#Speak to Sabjorn in the Honningbrew Meadery.
#Engage in some industrial sabotage and witness the mead tasting failure.
#Acquire the promissory note and return to Maven.

Detailed Walkthrough
Preparation
As you will be battling Ataxia-bearing skeevers, resist disease or cure disease potions or enchantments are useful. Furthermore, given the vermin's speed, a fast, light melee weapon is advised. Given Hamelyn's magical ability, resist magic, shock, fire, and frost spells or enchantments are useful.

Black-Briar Business
Now that you're a full member of the Thieves Guild, you've been told that Maven Black-Briar wants to see you. You are likely to find her on the second floor of The Bee and Barb. After a condescending greeting, Maven will solicit your cooperation in putting her competitor, the Honningbrew Meadery, out of business. She will also ask you to perform some industrial espionage to understand how Honningbrew could have started up their operation and achieved success so quickly. She will direct you to meet Mallus Maccius at The Bannered Mare in Whiterun for further instructions.

Meet Mallus Maccius
Mallus will tell you that Sabjorn, Honningbrew's owner, is planning to hold a special tasting for an important personage, and that you must poison the mead for the occasion. He suggests that you approach Sabjorn and offer to help him with a pest infestation, then use the poison he will give you to accomplish the deed. He instructs you to access the mead vats through a tunnel leading there from the meadery's basement. Although he claims you could alternatively pick the lock on the brewery door, you can't, as it requires a key which is only found inside the boilery. His own motives are quite simple: he'll be given control of the meadery from Maven once Sabjorn is out of the way.

Infestation Elimination
Sabjorn will quickly accept your offer to help and provide you with the required poison as well as the key to the Meadery. If you successfully persuade him, he'll even give you half your pay upfront (500 gold).

In the basement, you'll easily find the tunnel Maccius pointed as the infestation's source. Fight your way past the tough Venomfang skeevers as well as a few frostbite spiders, taking care to avoid bear traps and tripwire-activated swinging maces along the way.

You'll emerge in a large chamber where a mad bandit wizard named Hamelyn is guarded by several vermin. Try to use sneak to avoid fighting them all the same time, as Hamelyn can cast powerful destruction spells and is especially lethal if he catches you in a weakened condition. Poison the skeever nest next to Hamelyn's alchemy lab and don't miss the Sneak skill book Three Thieves lying atop a chest nearby. Press on, avoiding two bear traps, and you'll arrive at the door leading to the boilery.

Mellow Mead
Head up the stairs to a balcony overlooking the room and head towards the lone brewing vat on the far side. Poison it and exit using the Honningbrew Brewhouse key hanging on a hook on the right side of the door. Head back inside the meadery and you'll meet either Commander Caius or Sinmir (if the Stormcloaks have taken Whiterun) tasting the mead. The taster will sense something wrong with the drink and blame it on poor sanitary conditions. For this perceived offense, he will place Mallus Maccius in charge of the meadery and haul Sabjorn to jail at swordpoint.

Once Sabjorn has departed, speak to Mallus about gathering business intelligence for Maven and he'll hand over the key to Sabjorn's dresser. Head upstairs and steal the promissory note from the dresser. An expert-locked door nearby will open to reveal a room with some silver ingots, a silver necklace, some coin purses, and the Honningbrew Decanter, a miscellaneous unique item that can be sold to Delvin Mallory for a fair price. Be sure to read the Alchemy skill book A Game at Dinner, which is found on the table closest to the door.

Mysterious Missive
Head back to the Bee and Barb in Riften and report your success to Maven, who is frustrated by her inability to identify the note's author. When you point out the author's symbol is the same as that on the bill of sale previously found in the Goldenglow Estate safe she suggests taking it to Brynjolf. Provided you didn't kill anyone but Hamelyn, she will then pay you with a leveled enchanted sword or dagger. Once you're back in the Cistern, Brynjolf will muse that the identical symbol points to someone attempting to drive a wedge between Maven and the guild, and will send you off to Mercer to continue your search. Mallus will now also be available as a fence.

Notes
With a bounty of at least 1000 gold, the captain of the guard will try to arrest you on sight when you're reporting back to Sabjorn. Remaining out of sight and talking to Sabjorn is virtually impossible, so it's advised to bring the captain to his knees and quickly talk to Sabjorn, then remain undetected until the winetasting scene starts. It is recommended to stay hidden until the captain leaves with Sabjorn.

Bugs
 
  If you cannot obtain the quest, you can force it to start using the console with  , followed by  .
 
Changing to the third person view can sometimes resolve this. PC players can advance this manually using the console command  .
 
  If you cannot obtain the quest, you can force it to start using the console with  , followed by  .
 
 
 You can also transport Sinmir to the Meadery using the console commands   and  .
 

Quest Stages