Constable Underhill mentioned that there is a new threat in the Chetwood and that maybe it is the knight whom you seek.
'Golodir? I have never heard of him, but he sounds like one of those Rangers, like Toradan. If he's anything like Toradan was, I don't see any reason to doubt him.
'Well I'm not sure about this knight that you speak of, but there is a new threat in the Chetwood, much more powerful than anything you've come across in the past. Perhaps he is the knight you seek.
'You can find him at his camp near the evil idol in the Chetwood. It is not hard to find, north-east of here.'
The Knight of Mordirith can be found near an evil idol in the Chetwood, north-east of Combe.
Constable Underhill told you how to find the threat in the Chetwood, which might be the knight you seek.
Constable Underhill is outside The Comb and Wattle in Combe, south-west of the knight's camp.
Having defeated the Knight of Mordirith, you return to Constable Underhill and let him know that the threat is ended.