Data and Geordie are enjoying a Sherlock Holmes holodeck mystery, when Data's suave reveal is stopped in its tracks, as it turns out the suspect is apparently right-handed, when he's supposed to be left-handed. They stop the program and call Lieutenant Barclay in to check things out, who does a few diagnostics, then finds a locked program on the holodeck memory. When he asks it to run, who should appear but Professor Moriarty. It's been about four years since Data first granted him accidental sentience and he was subsequently left in the memory banks with a promise to find a way to free him, and he's not thrilled that it's taken so long, so he demands to meet Picard, who'd made the promise to help him.