Restless Activity is one of two quests that you pick up to start the quest chain that eventually leads to your acquiring [The Master's Key], which you need to enter Karazhan. The questgiver also gives you the other pre-requisite quest, Arcane Disturbances at the same time, which you can easily complete at the same time. Enter the Master's Cellar, down steps at (48, 78) for both quests