Defeat Morganth. Bring his Pendant of Shadow to Theocritus at the Tower of Azora in Elwynn Forest.
After much observation, I have discovered Morganth's plans.
He searches for the Scythe of Elune...and he may have found it! If he has, then the Redridge Mountains, and the kingdom of Stormwind, will soon feel his dark might.
I am not prepared to pit myself against Morganth, but I fear he must be dealt with now. So you must enter the Tower of Ilgalar and face Morganth.
Defeat him, and bring me his Pendant of Shadow. Do this, and the kingdom will owe you much.