[X] Send a messenger to the Kirin Tor with a letter detailing the nature of the threat and what you have learned so far while staying in the region to protect it and find Kel'thuzad. (Base gained next turn, will continue to fight in the Andorhall region, will lose 4 footmen 2 priests and 1 veteran sorcerer until they return and rejoin you, DC 30 if success Alliance leaders made aware of the scope of this new threat.)
[X] Go and report to the Kirin Tor about this new threat. (Arthas and Jaina split up, getting a new base delayed for several turns, cannon derailed, Alliance leaders made aware of the scope of the new threat.)