Operation: Castle took place during "Coup de Grace". It was Alex's first mission after being promoted to agent.
The target was Erik Mukhran, Prince of Georgia. His wife Kristina hired Division to take him out because she desired power.
Alex and a group led by Stephen seized a musuem exhibition and were supposed to eliminate the prince, however the mission was sabootaged by Nikita, who led the prince to safety.
The mission failed and Kristina is arrested for her involvement in the assassination attempt.