Star Trek two-parter The Menagerie gave the show's creator, Gene Roddenberry, an opportunity to make use of The Cage, his expensive unaired pilot for season one. Having set the scene in part one, with Spock charged with mutiny, part two largely comprises of footage from The Cage, as Kirk's loyal second-in-command uses images broadcast by the inhabitants of Talos IV to explain his uncharacteristic behaviour.
Having recently watched The Cage, I can't say that The Menagerie Pt 2 did much for me, the episode primarily a rehash of events from the pilot. The plot gives no adequate explanation for how Spock came to be in contact the Talosians, whose planet is a no-go zone, or how he was able to orchestrate and carry out his mutinous plan with such precision; in short, there are plot holes big enough to fly The Enterprise thorough. The uplifting ending - in which Pike goes to spend his remaining life in an illusory world created by the Talosians - makes little sense: why do the aliens feel so obliged to help Pike, who is no longer a prime specimen of humanity? Altruism certainly never seemed to be a Talosian trait.