Both the Alliance and Horde are interested in a weapon rumored to be possessed by Cho'gall and have sent an agent each into the Citadel area to investigate. The Twilight's Hammer has also captured and killed a number of red dragons, imprisoning one now familiar to players, Lirastrasza.
The Twilight Skyterrors fly above the area, untargetable until the Coup de Grace quest; even then, players are only required to kill them once they fall to the ground.