Because of the assistance of the ghost in the machine (the wizard who originally freed the Eye of Vecna from its binding), the PCs were able to get to Baron Trask quickly and without a fight, surprising him. With a little bit of tactical power use, they were able to keep the Baron’s undead bodyguard away from him until they finished killing him the first time—fast enough that annoying crossbowmen didn’t have a chance to make it into the throne room.
The Aspect immediately popped itself into a magic circle and went about performing the ritual for bringing over the Shadowfell-side ghoul army, the one that had previously been using the machine at the top of the tower. However, he called reinforcements (?), stone monsters of a type that could be forced through the circle to break it, and the PCs did so. (The reinforcements were pissy in that they immobilized PCs on succesfull attacks.) Verrick had a fun time keeping the Aspect busy, backing it into a corner, while the other PCs were trapped the stone monsters and busy beating them down so they could cross the room. Having done so, chasing the Aspect down and killing it was pretty simple.