Moriarty comes back and demands real life.
Lieutenant Barclay accidentally frees Professor Moriarty, the holographic villain from an earlier adventure. Moriarty, who has become self-aware, demands to leave the holodeck and enter the real world. He takes control of the Enterprise, and the crew has to find a way to stop him without destroying a living being.
Picard and Data devise a clever plan to trick Moriarty, using the holodeck itself as a trap. The story is a sequel to Elementary, Dear Data and a strong exploration of the idea of virtual life. The twist ending is clever and leaves the viewer with a lingering question about reality. It is one of the most popular stories of the sixth season.