2-04: Mirror, Mirror
A transporter accident swaps Kirk, McCoy, Scotty, and Uhura from distinctly opposite parallel universes.
2-26: Assignment: Earth
After traveling back to 1960s Earth, the Enterprise accidentally beams aboard a time-traveling secret agent.
2-06: The Doomsday Machine
Dispatched to investigate the destruction of several planets, the Enterprise encounters the badly damaged U.S.S. Constellation.