This quest is not available in game.
Kill 6 Kurzen Elite, 4 Kurzen Subchiefs, and bring Kurzen's Head to Lieutenant Doren at the Rebel Camp.
You have proven yourself time and again, and your resourcefulness seems to rival even that of Kurzen himself. You may be the salvation of our band of rebels...if you can pit yourself against Kurzen and prevail!
He commands his men from deep within the Stockpile. You must enter that cave, brave through his defenders, and face Kurzen and his leaders.
Farewell, <name>. My hope, and the fate of my men, go with you.