Vereth the Cunning on the Rise of Suffering wants you to kill Rokir, the Rider of the Unholy.
It's time that we start cutting off the heads of the beast.
I served beside Rokir for quite some time. He knows the unholy arts better than most any other death knight I've met and he's equally as ruthless.
Rokir's strengths are most apparent when you are fighting him on his own ground. Sadly, we don't have much option in those regards, but stay on your feet to avoid his undead minions and you should come out victorious.
Be nimble, [class], and do not take him lightly.