After talking to him, 3 mobs will spawn and ambush you. This will result in you being knocked out and ported to Drarson McCale's hideout in Halls of the Unseen.
Join The Circle of the Unseen Hand. (If you decide not to join the Circle, you will be knocked out again and then ported back to Butcherblock Mountains. You must talk to Drarson McCale again to continue the quest.)
To start the next quest, talk to Nyran Dudez ( 25, 3, 49 ) /waypoint 25, 3, 49 further down the corridor in the hideout. Do this before you leave the Halls of the Unseen.
To leave the Halls of the Unseen, click on the barrel along a wall just west of where you first enter the zone, at ( 60, 1, -4 ) /waypoint 60, 1, -4.