Betrayal from Within:

Kill Nak, Kuz, and Lok Orcbane and bring their skulls to Mangletooth at Camp Taurajo in the Barrens.

Mangletooth: Three of my tribe came out of the Kraul to lead the raids against the Horde, tauren. <snort> They are ruthless and cunning, and if you defeat them, then your Crossroads and even most of the Barrens will learn peace... <snort> at least from the Razormane tribe. <snort>

Nak, Kuz, and Lok Orcbane are the ones you seek. They are far to the south of the Barrens. One is a spell caster, another a tracker, and their leader, the one called Orcbane, <snort> a warrior. Kill them, tauren, like they have killed me.

Mangletooth: How goes your hunt, troll?

Thork thinks he knows the truth about who leads the raids against his people, but he shall learn how wrong he is if you are successful.

My death is inescapable, but you have caused great pain to my enemies, so Mangletooth regrets nothing.

Mangletooth: It is done then. Better it ends this way, says Mangletooth. <snort> They should have <snort> made sure I was dead when they turned their backs on me instead of leaving <snort> me here in this forsaken cage.

There is but one task left for you to finish, troll.