When I struggled with the Forsaken's poisons, I had a vision.  I had a vision of the druids in the Dor'danil Barrow Den, poisoned... murdered by the undead!  They are now errant ghosts, severed from their bodies and driven mad.$B$BSo that the druids' spirits might some day find peace, you must enter the Dor'danil Barrow Den and destroy its once great leaders: Taneel Darkwood, Uthil Mooncall and Mavoris Cloudsbreak.$B$BDo this, then return to me.