From wow.incgamers.com

Intro

Argent Emissary: The time has come for Horde and Alliance to look towards Northrend and the invasion of the Lich King. In recent days, territories across Kalimdor and the Eastern Kingdoms have come under attack. Will you take up arms to save your land from destruction at their hands?

Quest

The quest is given by Argent Emissary located at Light's Hope Chapel near the Alliance gryphon master.

Argent Emissary: Excellent, an experienced adventurer. Precisely what we need.

There has been talk from the Kirin Tor guarding Medivh's tower that something is amiss with Karazhan. There is a new power lurking within, one that answers neither to the Guardian's magic nor the Legion. From what they've scouted, it appears it is an elven prince called Tenris Mirkblood, and there is reason to believe he serves the Scourge.

Go, my friend, investigate Mirkblood's chamber, and return with any information you might find.

Quest Objectives

The Argent Dawn Emissary wants you to search the chamber of Tenris Mirkblood within the Servant's Quarters of Karazhan.

Rewards

Monster Slayer's Kit (trinket) - Use: Throw one of the many weapon in the Monster Slayer's Kit at the target. (1 Min Cooldown) Requires level 70.

Inscription: "Everything from silvered knives to holy water."

Prince Tenris Mirkblood

He may be found at the Servant's Quarter in Karazhan. Clear your way through Atummen and go upstairs through the stable.