1-28: The City on the Edge of Forever
After following a delusional McCoy into 1930s Earth, Kirk must make a heart-wrenching choice to save the future.
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.
1-27: The Alternative Factor
Enterprise encounters Lazarus, whose behavior is representative of two drastically different personalities.