Kill the druids: Taneel Darkwood, Uthil Mooncall, Mavoris Cloudsbreak; then return to Kayneth Stillwind in Forest Song.
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.
So 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.
Do this, then return to me.