This quest was marked obsolete by Blizzard and cannot be obtained or completed.
Go to the front gates of Stormwind, read King Wrynn's Proclamation and search 5 Stormwind Citizens. Keep anything suspicious that you find.
After your work in dealing with the Twilight's Hammer cult, Captain Anton recommended you for a delicate assignment.
My men recently discovered a group of cultists attempting to sneak into the city. The flow of traffic into the Stormwind has come to a halt. The king has decreed that all visitors must be searched before they can enter the gates. Take this copy of his proclamation and read it to the people assembled at the front gates, then assist the guards there in searching those who wish to enter.