The Dainty Sload (quest)

Walkthrough
You will receive this quest after completing 5 Radiant Thieves' Guild quests in the city of Solitude.

Speak to Erikur
After getting this special contract from Delvin Mallory head to Solitude and talk to Erikur who can usually be found in the Blue Palace.

Apparently Captain Volf of the Dainty Sload has broken a trade agreement with Erikur, and Erikur wants to teach the captain a lesson by planting Balmora Blue, a highly illegal substance, in his footlocker. The authorities will then arrest Volf. The footwork is up to the Dragonborn of course.

Acquire the Balmora Blue
Find the first mate of the Red Wave, Sabine Nytte, at the docks and pay her 1,500 for the Balmora Blue, then go grab it from the chest under water, under the dock decking, near the ship.

Alternately, if the Dragonborn does not have the coin or the inclination to pay such a ludicrous sum: pickpocket Sabine and grab the Red Wave Safe Key to her safe on the lowest deck of her ship, the Red Wave. The Balmora Blue Note in the safe then points at the location of the chest with the Balmora Blue. Sabine's Footlocker Key comes in handy here.

Plant the Balmora Blue
Travel to the Dainty Sload in the north-east, then sneak on board until reaching the Captain's Chest and plant the Balmora Blue to then leave the ship again.

Tip: All this should be easier without a follower in tow. Potions of Invisibility should also help.

Return to Erikur
Return to Erikur, who will be delighted, promising not only to support the Thieves' Guild in Solitude but also rewarding the Dragonborn with a (measly) Spell Tome: Courage.

Consequences
Delvin Mallory will be pleased with the outcome, assuring the Guild's foothold in Solitude.

He will also mention that the alchemist Herluin Lothaire has taken up residence in the north-west cell, just outside of the Ragged Flagon, adding an alchemy lab there.

Die Holde Kreckin (Aufgabe)