Kill the Dalaran archmage, then retrieve his staff for Shadow Priest Allister at the Sepulcher.
An archmage of great power is overseeing the reactivation of the ley energy node. With the progress they have made, our only hope of stopping them is by killing him. It will be difficult, he is no doubt protected by many other mages and warders.
You must go, and you must dispatch him quickly. When he is dead, retrieve his staff for me. Go now.