Find the Argent Dawn member near the entrance to the Undercity.
Not sure if you heard, but two emissaries of the Argent Dawn just passed through here. I don't mind the Argent Dawn, but I don't like them poking around Tirisfal unsupervised either. They were both Forsaken... but that doesn't make me any less nervous.
One of them just passed by here, headed southeast. There's a group of scourge cultists snooping around the outskirts of the city in that direction. If those two heard about them, there's no doubt that would have caught their attention.