Take Luther's Journal to Shadowstalker Barthus at Warsong Hold.
You skim through the pages of the book, looking for anything of importance. On the last page you discover what appears to be frantic scribbling:
Necrolords. At least a dozen by my count.
Farms to west being used as some sort of horrible spawning glade for Scourge.
Row upon row of victims.
I think they're on to me. Made a dash for the hold. I won't be captured alive.
Dreadvenom hemotoxin. If they decide to bite into me, they'll be in for a surprise.
Take this information back to Barthus.