1-05: The Enemy Within
A transporter malfunction creates two distinctly opposite Kirks.
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.
1-29: Operation: Annihilate!
A planet, home to Kirk's brother and nephew, is under attack by unique creatures.
On a planet resembling 1960s Earth, all of the adults have perished from a deadly disease.