The nazgul are up to no good again. Time to open an investigation.
Which is to say, follow Eltariel until she leads you to the local Nazgul. This one's Isildur, apparently, and he raises an army of Gondorian wights to fight you.
Wights aren't so tough. They have to be dodged rather than countered, but they can still be vaulted, frozen, and shot in the head.
Destroy this lot then move onto destroy the next, with a bonus objective of not being detected.
This is certainly possible with Wraith Vision, and the payout of 750 Mirian is pretty high, compared to other optional objectives. Still, it is just Mirian at the end of the day, so if stealth isn't your favorite thing, just put the time you save here into a warchief mission or two later. If you do go on the hunt note that,even out of Wraith Vision, each enemy has a convenient yellow plot diamond floating over their heads. Also nte that most of your usual execution look like banishments now- don't let it throw you.
When the last one has been accounted for, by whatever means, follow Eltariel.
She'll lead you to Isildur, who attacks with morewights. As usual for a nazgul fight, keep the focus on the ringwraith. However, because wights are so fragile and they can't be Countered, do go ahead and destroy any nearby when you get a chance. Use standard tactics against Isidur until he starts deploying a teleporting explosive attack. This can't be countered, so run to the Light of Galadriel as instructed.
A brief cutscene plays, and Isildur will summon more wights, this time led by old Castamir.
Castamir is tougher than the other wights, but no more dangerous. Take down the no-names first, then rebury the betrayer of Minas Ithil. Not that you have to do much work- Eltariel will keep up a steady stream of attacks from the side lines.
When he falls, the mission completes.