Season 7, Episode 23 - "Emergence"
Stardate: 47869.2 When strange occurrences occur on Enterprise, the investigation leads to the Holodeck, and an independently running program there. A train is traveling to an unknown destination, which the train crew will not allow any deviation to be made. The Enterprise crew soon learns that all these events are related to the emergence of a strange new life form which may endanger Enterprise.
