Speak to A'dal in Shattrath City.
You have proven yourself capable of great feats, <name>. Your discovery of the Cipher of Damnation and Kael'Thas' involvement is most important to our cause. Should Kael use the cipher, what little is left of this world may collapse.
A'dal is convinced that Kael must be stopped and now seeks adventurers willing to undergo trials. Those that prove their strength will be granted the Tempest Key.
The naaru's key to the vessel.
Tempest Keep is a naaru creation, mortal. Access to the vessel has always been within our power to grant. A return to Tempest Keep, though, had been deemed unnecessary. A point of pride for a mortal race, perhaps, but naaru invest little in such things.
We go now because we must. Kael'Thas cannot be allowed to utter the words of damnation.
This is quest chain. Prerequisite: The Cipher of Damnation quest chain