The corruption out of Angmar has angered and misguided many of the creatures in The North Downs, including Dúrlum, a disturbed spirit of Fornost.
'The enemy forces occupying Fornost have angered and corrupted even the dead. Recently a powerful shade has begun stalking the Fields. The Orcs must have been searching the deepest of tombs. Now even the Orcs are afraid of the one they call Dúrlum. This spirit must be put to rest.'
Dúrlum can be found somewhere in The North Downs.
You should defeat Dúrlum.