Speak to Taran Zhu in Bleak Hollow.
The Shado-Pan arrived here before we did, and they are already at work undermining the Thunder King's forces.
I want to you meet with Taran Zhu, the leader of the Shado-Pan, and offer your services on behalf of the Sunreavers. I doubt he is truly in need of the aid, but the gesture holds importance in itself.
You will receive: 19 84 50
Use the teleporter on deck to reach Court of Bones and cut through the Zandalari troll-infested territory. Follow the road to reach The Emperor's Gate.
Immediately west (to the left) of the gate is a cave, the Bleak Hollow, which the Shado-Pan has claimed as their base.
Taran Zhu's followup quest,  Secrets in the Isle of Thunder, is not part of the main progression, but it is something to do while otherwise questing.
- Stage 0:
-  Thunder Calls
-  The Storm Gathers
-  Allies in the Shadows
- Stage 1:  The Assault on Zeb'tula
- Stage 2:  Tear Down This Wall!
- Stage 3:  To the Skies!
- Stage 4:  Decisive Action
- Stage 5:  The Fall of Shan Bu
- At exalted: [90R] Life Blood