The Obsidian Dragonshrine

Travel to the Obsidian Dragonshrine northwest of Wyrmrest Temple and just west of the Wrath Gate. Locate Serinar there and offer him your aid.

The Scourge come. Korialstrasz calls upon his allies in a futile attempt to save their Ruby Dragonshrine, but it seems the good graces of the red flight don't extend to saving the shrines of the other flights.

Surprised? I'm not.

There is another of my brood who has left to clear our Obsidian Dragonshrine and the undead vermin that now infest it. All it would take to prove yourself more noble and righteous than Alexstrasza herself is a quick jaunt over there and a few swings of a blade.

I'm amused.

I'm trying to decide at which I'm more surprised... that you actually came to the aid of a Black Dragon or that you're still in one piece after speaking with Nalice.

Her words drop venom, but I suppose Wyrmrest can keep even our kind in check sometimes.

Or perhaps it's just the armies of the red dragonflight that are massed around her.

Serinar is inside the Maw of Neltharion.