You... and Your Shaaaadow.

Shadow Labryrinth instance guide is here. Entry in to Karazhan is a quest chain that will be illuminated in the following post on The Master's Key. The Soul Devices can be acquired off of the Spy mistress at Shattrath (that doesn't abreviate well) or probably shared. I believe the other two can be picked up outside the instance but don't quote me on that. Everyone should have a key to the Shadow Labrynth door, it was in the chest at the end of the previous instance we ran.