The Menagerie parts one and two was the only 2-parter during the 3-year run of the original Trek series and it was because Roddenberry was able to insert most of the footage from the 1st pilot "The Cage." The move was made out of necessity, to combat deadline problems in getting episodes produced (such a sf show back in the 1960s was a hassle to get done on time). One positive outcome back then was that audiences, unaware of the pilot produced almost a couple of years earlier, were treated to a whole new crew and captain for these two episodes on top of the regular cast of characters, as if the producers had spent double the money on these episodes to present a TV epic spanning a dozen years of Starfleet history (though they still used terms such as 'United Space Fleet' in these early episodes).
The wraparound story begins as a space mystery plot: the Enterprise is diverted to Starbase 11 for unknown reasons and very soon Spock is a suspect in these shenanigans. Astonishingly, though even McCoy belabors the fact that Spock's Vulcan heritage makes subterfuge on his part impossible, it does turn out that Spock is indeed acting out some mutinous scheme to shanghai our precious starship and kidnap his former captain, Pike, now horribly crippled. Well, Spock is half human, we tend to forget. Or has he simply gone mad? It may very well be, for he's directing Enterprise to Talos IV, a planet so off-limits it's the subject of the only known death penalty on Starfleet's books. When the jig is up, there's a great scene of Spock surrendering to a flabbergasted McCoy, as Uhura looks on in shock. Even Kirk, usually steady as a captain should be, doesn't know what to make of his first officer's illogical conduct.
In the 3rd and final acts, we begin to see transmitted images of a mission of the Enterprise from 13 years prior, when Capt. Pike was commanding and Spock was one of his officers. We really don't know where all this is going and what Spock hopes to accomplish - and that's another thing that makes this a very good 2-parter - we really need to find out what it's all about in the 2nd part. Not only is Spock facing severe penalties, but it looks like Kirk's career may be finished, as well. Double jeopardy, folks. This is also the 1st televised episode to feature one of those shuttlecrafts (none were available in the earlier "The Enemy Within" when the crafts were really needed). There's also one of those neat matte paintings to convey the ambiance of a futuristic starbase - this was the only way to visualize such things back then. Finally, check out Kirk's smug approach at the start of the episode - boy, do things go sideways on him as the story progresses.
