This quest is not available in game.
Kill 12 Syndicate Footpads and 8 Syndicate Thieves, then return to Magistrate Henry Maleb in Southshore.
I am the new magistrate of Southshore, recently assigned after the assassination of the previous magistrate. The assassins were never found, but through our investigations we're almost certain they were hired by the Syndicate - a group of thieves led by villainous nobles of the now fallen kingdom of Alterac.
The Syndicate has a camps in Sofera's Naze and Corahn's Dagger, north and west of the Horde-occupied Tarren Mill. Slay the Syndicate members you find in these camps.