An ancient people who fled their dying star aboard Yonada, a hollow asteroid ship whose passengers forgot they were travelling at all.
The Fabrini lived around a sun that went nova thousands of years ago. Before the disaster they built Yonada, a hollowed-out asteroid fitted as a generation ship, and sent their descendants toward a new homeworld. Over the centuries an artificial Oracle ruled the inhabitants, who came to believe their world was a planet.
The Enterprise found Yonada on a collision course with an inhabited world. McCoy, who had a terminal illness, fell for the high priestess Natira and married her, and the crew corrected the ship's course. The Fabrini medical records aboard Yonada provided McCoy's cure.