Investigating the Halls

If the quest bugs for you, in my case Magni did not move at all. Abandon the quest and retake just outside the entrance.

Okay, I had to do this quest four times before I worked out how to do it.

When you enter the Halls of Origination you'll be in the entrance passageway. Take a step forward and it'll start collapsing; there's some talking and you're transported out into Ptah's tomb. Walk outside and there's some whirlwinds and an alter to N'Zoth. When you approach the alter it'll push you backwards. When you click on the alter you'll enter a tiny vision of N'Zoth

Now, what I was doing was running straight over to the alter and clicking on it. Because I was a death knight I used Death's Advance and its pushback didn't slow me down. Don't do that. The vision will activate but you won't hear Wrathion. Killing the mobs doesn't help. Trust me. I spent five minutes kiting the elite to death.

Wait for Magni. After you appear in the tomb he runs over to a teleporter and activates it for some reason. Then he slowly runs across the courtyard. Then he very slowly walks up to the alter. Wait for him to get there. He should have three voice lines, and until I waited for him I was only hearing the first.

Magni Bronzebeard says: Look! Across the sand! That must be the anomaly!
Magni Bronzebeard says: Wait... do ye feel that? Somethin's wrong...
Magni Bronzebeard says: Be careful, hero!

You'll know it's worked if Wrathion starts talking once the vision activates. From other comments on this page, you don't actually have to dismiss the whispers to complete the quest. Dying from sanity loss will work too. If it bugs out you can just abandon the quest. You'll be transported outside and Magni will be waiting to give it back to you.

so she could teleport us to Magni this whole time and yet we've been flying and porting back and forth for the last bajillion quests?