2-04: Mirror, Mirror
A transporter accident swaps Kirk, McCoy, Scotty, and Uhura from distinctly opposite parallel universes.
2-17: A Piece of the Action
Enterprise discovers a gangster-run planet similar to 1930s Earth.
2-23: The Omega Glory
The Exeter is found drifting in space, its crew dead from a mysterious disease, except its missing captain.
2-06: The Doomsday Machine
Dispatched to investigate the destruction of several planets, the Enterprise encounters the badly damaged U.S.S. Constellation.