Taking away their pendants is just the first step. If the Kirin Tor really are shipping a steady supply of relics from Dalaran, we must stop them at the source.
Search the roads around Ambermill for Dalaran's wizards and watchers. Their presence has allowed free access across our borders for too long. If we can cull their numbers, that should put a stop to these pendants making it into Silverpine Forest in the first place.
