Your official return to what was Minas Ithil (though it's possible to complete a Carnan quest here first). Meet with Eltariel and follow her into the heart of the city.
Your subgoal is to dominate 15 orcs. You'll encounter more than 15 orcs on your way in, but if you want to avoid those fights or just like to play it safe, you can use Shadow Strike Pull to snag in distant victims from the bridge behind you, or from the towers you pass under.
Once you hit your quota, there's no more reason to engage with the orcs you pass, just keep following Eltariel.
She'll eventually lead you into a fight with the Ring Wraith Suladan, and his posse of orcs.
The key to this fight is to focus on Suladan- ignore or evade the orcs while watching for his moves. He has the same attacks as before (the teleport stab and the care bear stare), as well as two new ones- a curse effect that hits anyone not standing next to Eltariel (she'll call out when you need her protection), and an area effect last marked by an explosive icon and a green circle.
Frankly, the curse effect isn't so bad. The strategy here is to keep evading the orc mob while watching Suladan. When he's about to attack, counter, then follow up with your own attacks. Sometimes he'll back off, sometimes he'll ready a swing that you SPACEBAR dodge, then continue your counterattacks. These are the only things that hurt him, so just keep watching for those chances, while dodging his balefire bombs and any nearby orcs.
It's tempting to drain the orcs for health and ammo, but Suladan rarely gives you enough time, so spare yourself the temptation and just focus on the main man himself. When you've finally taken down his health, you'll be able to banish him as before. This triggers a long cutscene on the origin of Nazgul, and mission completion.