Frideric the Elder has warned you of a new threat in the southern bogs and that maybe it is the Knight you seek.
'I have never heard of Golodir, but if he is a Ranger, as you say, then why should we give aid to him? The Rangers did not aid us when we had a need, and we were forced to rely upon the shades of Oathbreakers to win our freedom.
'Still, we have lost many good men exploring Harloeg these days. There is rumour that Angmar is involved, so my guess is that is the best place to search. Go to Harloeg and seek out your evil Knight.
'When you have purged this evil, return to me.'
The Knight of Mordirith may be found somewhere within Harloeg, south and east of Ost Guruth.
Frideric the Elder suggested that you might find the Knight of Mordirith in the southern bog.
Frideric the Elder is at Ost Guruth, north and west of Harloeg.
Having defeated the Knight of Mordirith, you should return to Frideric the Elder and let him know of your success.