The Kergrim of the Morgul Vale seek to conduct many foul rituals, and will not stop until they have managed to raise the dead.
'These structures were not fashioned by the hands of Men. The kergrim seem more organized than the beasts you have encountered in days past. Whatever their plans are, you must stop them. Seek out the chamber in the barrow where Shalgoth seeks to perform this ritual. I will make certain that no kergrim enters the barrows to ambush you from behind.'
Shalgoth fled into the deep-barrows of Gorthad Nûr.
You should confront Shalgoth and stop the ritual.
Thurindol can be found at Echad Uial in Rath Dúath.
You should talk to Thurindol.