They're building a second mana bomb in the courtyard.  My intel suggests that the final code for the bomb is being held by Sharth Voldoun, the overseer of the project at Firewing Point.$B$B$N, you have to go back in there and retrieve the final code from him.  He keeps himself to the top of the highest spire.$B$BTake the final code to the mana bomb that they're working on in the central courtyard and set it off.$B$BOnly then will we be certain that the Allerian Stronghold is safe.