Moonrest Gardens Plans can be found on the corpses of Dragonblight Mage Hunters and is a quest objective for:
Text of the correspondence
I am sending a representative of the Ethereum to you. Ambassador Duyheen tells me that there are more of his kind who would like to join the cause. Feel him out, see if you can find a use for him.
If he proves helpful, I may consider accepting more of his kind into the fold.
Don't be an idiot; burn this letter once you've read it!
Patches and hotfixes
/ Patch 3.0.2 (14-Oct-2008): Added