Elementary, Dear Data

With time to spare before meeting the USS Victory, La Forge and Data try a Sherlock Holmes mystery on the holodeck. Data, who knows every story by heart, solves it at once and spoils the fun. When Dr Pulaski scoffs that he could never solve a truly original case, La Forge tells the computer to create an adversary capable of defeating Data. The result is Professor Moriarty, who kidnaps Pulaski and then begins to grasp that his world is an illusion. Reaching into the ship's computer, he makes a drawing of the Enterprise and takes control of vital systems. Picard enters the holodeck to negotiate. Moriarty, now truly self-aware, asks to leave the holodeck and exist in the real world. Picard explains that this is impossible, but promises to preserve the program until a way is found. Moriarty releases the ship and lets himself be saved, while the Victory arrives at last.