See Nightbane quest chain for a summary of this quest chain.
Go to the Master's Terrace in Karazhan and use Kalynna's Urn to summon Nightbane. Retrieve the from Nightbane's corpse and bring it to Archmage Alturus.
You will need:
Our preparations are complete. I have put the materials you gathered into this urn. Take it to the Master's Terrace, where the fight took place, and set it on fire.
The energy released will bring life back to the charred remains of Arcanagos. Defeat the creature and retrieve its essence immediately! You will need to take it to Alturus.
Should you fail, the stars predict you will have let a great terror loose upon the skies.
A terror known as Nightbane!
What news do you bring, <name>?
If you do not manage to kill Nightbane, but run away to the door, you may be able to leave combat, but the Blackened Urn will no longer be there. If you are saved to Karazhan, you will have to wait until the instance lock expires before you can try again.
This is astounding! Not only have you brought back Medivh's Journal, but you've also retrieved a fragment of his very essence.
As faint as this lingering essence is, it will reveal to us vital information about Medivh. We will not forget this, <class>.
- +3000 reputation with The Violet Eye
This is part of the Nightbane quest chain: