1x6 - The Starlost

This episode is set in a lavishly appointed spa in a dome called New Eden Leisure Village. At first it seems completely deserted, but Garth hears someone moaning. He finds a young girl seemingly in a state of shock and attempts to find out what's happened. The girl will not speak. However, Rachel is able to gain her confidence and determines that something horrible frightened everyone else away, and she was left behind in the confusion. The trio decide to stay and try to solve the mysterious evacuation.