Deep within the halls of Moria, flames lick out of oily pools. It is here that the Ghâsh-hai make their home. A faction of these is aligned with the master of Moria, Mazog, and has come to the Grand Stair to pay tribute to their leader.
'While the Ghâsh-hai prove to be a potent foe, they too have leaders, and theirs made his way into the Grand Stair some time ago.
'The Ghâsh-hai tend to gather near flame. When you make your way to the Grand Stair, search for a source of flame, and there you will find their leader, Gothghaash.
'Find him and destroy him, so that we might more easily remove the foe from the Grand Stair. Travel north-east from the Orc-watch to find the entrance to the Grand Stair.'
Gothghaash can be found within the Grand Stair, north-east of the Orc-watch.
Ossur told you of Gothghaash, the leader of the Fire-orcs, and directed you to find and defeat him.
Ossur is at the Orc-watch, south-west of the Grand Stair.
You should return to Ossur at the Orc-watch and tell him of your victory over Gothghaash.