On a planet resembling 1960s Earth, all of the adults have perished from a deadly disease.
1-03: Where No Man Has Gone Before
An incident on the edge of the galaxy transforms two crew members, one of whom is a long-time friend of Captain Kirk.
1-07: What Are Little Girls Made Of?
The Enterprise finds Nurse Chapel's long-lost fiance, Dr. Roger Korby, living isolated with advanced androids.