There's a lot of hints in game :
- Velen taking the exodar to Argus
- Illidari talking about attacking Argus
- Turalyon who sent the Light's Heart on Azeroth is fighting with the Army of the Light on Argus
- Xe'Ra telling us that we must find Illidan to help the Army of the Light
- Medivh in Karazhan telling Kadghar that sometimes it's safe to close a door (talking about the gate in Karazhan leading to the Twisting Nether) but sometimes it's better to go beyond that door and fight what's behind.