Collect a Dark Parchment from the Shadowmoon Burial Grounds.
We have reviewed Ner'zhul's notes, which you brought to us previously. Though we are closer to understanding how these warlocks have learned to bind souls and control the undead, the picture is incomplete.
We will need more pages if we are to see the whole picture. I do not want to experiment with partial information and create an abomination. There are enough of those in Northrend as it is.