The Defias Brotherhood
Kill Edwin VanCleef at the end of the dungeon and bring his head to Gryan Stoutmantle.
Kill Edwin VanCleef at the end of the dungeon and bring his head to Gryan Stoutmantle.

The chain before it is long and travels to Lakeshire and Stormwind, so start it well before the run.
VanCleef also drops An Unsent Letter, which starts its own quest.
Alliance: Gryan Stoutmantle in Westfall (56.3, 47.6).
Alliance: Gryan Stoutmantle in Westfall (56.3, 47.5).
Chausses of Westfall, Tunic of Westfall, Staff of Westfall, 6,200 XP.
The Defias Brotherhood is a level 22 quest; you can pick it up from level 14. It takes you into Deadmines.
Sources: Quest data from ForeverDB.net · ForeverDB: Deadmines dungeon · ForeverDB: Westfall quests · ForeverDB: Stormwind City quests · ForeverDB: The Defias Brotherhood · ForeverDB: Underground Assault · ForeverDB: The Test of Righteousness · ForeverDB: The Unsent Letter