WARNING: This thread WILL contain unhidden spoilers for this entry. Because this re-watch is in a slightly-subjective chronological order and not in production order, please refrain from talking about the content of other episodes or movies in this thread. If you do, please put that content inside spoiler tags. Some people here may be watching Star Trek for the first time.
#17: Star Trek: The Original Series, season 1, episode 11 & 12 "The Menagerie"
Written by Gene Roddenberry, directed by Marc Daniels & Robert Butler.
Stardates 3012.4 through 3013.2 (September 2267)
"It's your life now. At least a chance for life." - Commander Spock
The Enterprise is called to Starbase 11 by an urgent summons. However, when they arrive Commodore Mendez (Malachi Throne) reveals that they sent no message to the Enterprise. While on base, Mendez reveals sad news to Captain Kirk, and especially Commander Spock - Captain Christopher Pike (the man who commanded the Enterprise prior to Kirk, and Spock's former Captain) has been gravely injured in an accident and is undergoing treatment right there on Starbase 11. When they go to see him, Pike is a shell of his former self and demands everyone except for Spock leave his quarters. When Kirk & Mendez suspect that the message was sent by Pike himself, Mendez reads Kirk into a top secret report about Pike's mission to a planet called Talos IV and how it is now forbidden for any starship to travel there. While they are talking, Spock reboards the Enterprise with suspicious, classified orders to embark for Talos IV immediately... leaving Kirk behind.
Originally released: 17 & 24 November 1966
"The Menagerie" on Memory Alpha part 1, part 2
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What did you think?

Visual effects comparison of the original broadcast & the Remastered versions.
https://www.youtube.com/watch?v=WnpO7dOSOTg
https://www.youtube.com/watch?v=-ml6xKkL6o0
https://www.youtube.com/watch?v=JwJ9Ey_WXx0
https://www.youtube.com/watch?v=G3Kx4X2qcI8
https://www.youtube.com/watch?v=ffgrUYeqtoE