Once back in Citadel of Pain, South, there is a
short path between you and the shard. Kill the creeps and
tormenters, and grab the shard. Head back to the portal, and go to
Plane of Torment, East. All that is needed here is to go talk to
Gol Nazyn. Mister Nazyn will tell you some of the story; of
course, you have already guessed most of it. Once you talk to
him, head back to the Plane of Tranquility.