ST:TOS:16a - "The Menagerie Part I" (Stardate: 3012.4), the 16th episode to go into production but the 11th one shown on TV, this is the first of a 2 part episode which took the original Star Trek pilot called The Cage and expertly intertwines it into a current storyline involving Mr. Spock seemingly betraying his captain and ship to take his former captain, Christopher Pike (who was only in the original pilot, whom they later replaced with Kirk) to the forbidden planet of Talos IV - through the Enterprise TV screens you get to see the event of this rejected pilot (an event that is 13 years before the present time - you get to see a more emotional younger Spock too in those prior events!). And the cliffhanger leaves much to be answered and you definitely will want to stay to watch part II. And, all in all, a brilliant two part episode, which was honored with a Hugo Award for Best Television Sci-Fi Program.
Review of The Menagerie: Part I
