Upon receiving the remnants of the ancient ward originally used to keep Borangos at bay, Isnír wishes for you to return to Nargroth in the hopes of learning more about the domain of Great Rogmul.
'${PLAYER}, I have something I would like to share with you. I have been looking through my notes here and have come to a few truths about these ancient fragments you have brought back from Nargroth.
'From the visions you have described and from what I have learned of Nargroth, I believe that the fortress of Nargroth was built on top of something else. It seems that Nargroth has been a mighty structure in Mordor for many years. What was built in the Caverns of Fire before Nargroth's construction is much, much older. Looking at these fragments, I would say it is of a chamber of some kind. Perhaps with a ward or seal. I would put this structure as being built around the Second Age. Possibly early Second Age.
'From what you have told me, I believe all this has something to do with Borangos. This Rogmul is most powerful. In historic text, none have been seen such as Borangos since the times when great beasts of fire and shadow walked the lands for Regmyl to serve.'