Terror from Beyond is a level 55 operation mission. It is obtained on the Imperial Fleet by speaking with Colonel Jadick on the mission deck of The Ziost Shadow.
||The Gree world of Asation has suffered an attack from unknown aggressors; worse still, the invaders have begun to open an ancient Gree hypergate, allowing things that have been sealed away for millennia to pass into the galaxy. The Gree have begged for intervention as they do not have the martial resources to restore order.
||~ Star Wars: The Old Republic, Terror from Beyond mission description